Having just done what you are about to go through.....I'll tell you....prepare yourself...unless your shop physically has all the parts on hand that you will need, I'd be shocked if you have your engine back in 3 months. It took 8 to turn mine around and just got it back flying 3 weeks ago. I also said oh yeah 3 months tops when I started in September. That being said I hope your shop is right and you flying again in 3 months.
The plus side to being down for 8 months in the winter in Chicago....I completed quite a project list on my 8KCAB. Everything firewall forward was either replaced or overhauled. I installed new carbon fiber floors (except baggage floor board-covered that with carbon fiber vinyl to somewhat match), a complete new interior and all trim pieces, disassembled seats- powder coated them and reassembled with new bushings and hardware, smoke system, SL 418 Electrical update, new Mitchell oil temp and pressure gauges, replaced the fuel shutoff valve with the new style current part, and replaced and updated just about anything else that mounts on, goes through, or touched the firewall. Also overhauled the prop and flushed the inverted system. All new oil and fuel hoses, overhauled mags and fuel injection system. Replaced the rudder cables (both had a frayed spot)- was going to replace elevator cables, but that's nearly impossible with the fuselage covered and mine are in great shape, and repainted the wing struts and gear legs. Plus a few other things I'm forgetting. If you send your mount out to be overhauled to AMI (there are pretty much the only ones left, they bought out everyone else), it will cost you about $1700, no matter what they quote you when you send it in. If you can strip and paint it yourself and find a local guy to inspect it you are way better off and prob only looking at a few hundred bucks.
As far as the firewall goes, that can be a rabbit hole....and I'll tell you my story lol. You can order one from Wag Aero, be prepared for it to take 8-12 weeks to be made and its galvanized like the old ones, and also be prepared for it not to fit well and come to you without any holes drilled in it. You can also get a new stainless firewall from ACA for 4 times the price. This is what I did and it was well worth it. It already has all the holes you need punched out and you can get new passthrough covers and grommets with it. In fact I would order it completely made up in the factory and shipped to you with all the new shiny parts attached to it already. Someone on here had an 8KCAB firewall made up they didn't use and was selling it in the last month or two. Had I seen it a few weeks earlier I would of bought it! So if its still available, I would snag that one! The new firewall becomes a rabbit hole when you find out that the gascolator pass through has changed, as well as the starter cable pass through hole when you do SL 418... so I ended up replacing my fuel shutoff valve, gascolator, and associated fuel tubes because I did not want to put a bunch of extra holes in the brand new firewall I just bought. And this way my airplane has current parts that can be easily obtained if need to be fixed or replaced. Oh and did I mention....the new fuel valve requires a new bracket be welded to the frame in place of the old one. Not that big a deal, but you will need a welder who knows what they are doing. We have a great guy up here who did it for me as well as welded in the second seatbelt lug in front for the hooker harnesses. I also got new heat boxes (front and rear) for the firewall as well as new insulation on the inside. In fact I replaced all of the boot cowl insulation while I had it opened up.
The electrical mod is not hard with the plane all opened up, the one thing I will say is that look at your battery tray before hand. If it is the old Bellanca tray still, then you will prob need a new one, unless you are going to patch the hole cut out of it next to your current master solenoid. There isn't enough room on the old tray with the hole to mount both the master and starter solenoids. I also replaced the long thick starter cable that runs from the back, through the firewall and to the starter. This was cleaner and easier than using the existing cable.
The one thing I didn't do, cause I was already maxed out paying for a new engine and all the upgrades and part is install a JPI or EI engine monitor. Don't be me....install one!!!! Thats the one regret I have abut my 8 month project. I was saving it for the future panel redo and upgrade next winter. Would be very helpful right now while I'm breaking in my new engine!
So as far as what to absolutely do?....How much free time do you have? lol. Everything I did took the course of about 3 months really working on it a solid full 3-4 days a week. I did almost all of it myself with the close supervision of my A&P, and it turned out great. Must do's though for sure...spruce up anything you can firewall forward. Especially overhaul or inspect the mount and replace the Lorde mounts. The firewall and everything else it caused me to modify was prob the biggest part of the project believe it or not. That being said, it could be done a lot simpler and faster I'm sure by not messing with the fuel system at all. Take out the crappy old carpet and wood floor boards and go carbon fiber if you have the money. And for gods sake, yes definitely do an engine monitor now!
Oh, and I also have the convenience of being an 18 min flight from the factory. I prob made 15-20 runs up there for parts and to be able to look at how things go together and ask questions.
Hope this helps. I have a ton more pics if you need of anything I've done.
Brian
I thought it was at TBO.