Congrats on your retirement.
There are a few great options out there and I'm assuming that you're not interested in building the motor yourself.
So with that in mind, the first question is what do I want the engine to do (mission)? If you are looking for a roadster to look great and move quick, you can go with a 302 or 306. If you want originality or mega horsepower, you can go with up to a 427. My mission was to have a car that will in the end look great but also be formidable on the street. So what I did was I went with a BPE 347. Cost per HP is the best with that option with you consider all the engines and cost.
I added the option of carbureted and added the TKX transmission in. From Order to delivery date it was March to June. Everything comes with that set up, it's dyno'd and ready to plug and play (literally).
I bought my rear end axle from Forte's. That also comes completely ready, brakes, brackets, everything. And I know Forte's sells engines themselves and if you go with his engines I'm confident you can't lose there either. I highly recommend him and from what I see in the forum, his Coyote package is awesome.
I ordered my FFR Roadster kit in March and it will not arrive until August. Until then, I've ordered (and received) everything I need to finish it, engine, transmission, rear axle, etc. That way when it gets delivered there's no waiting around (except for what may be on the POL list from FFR).
Good luck, looking forward to seeing your progress!