52,
With enough persistence, skill and resources, you can put about any engine in anything. However, I assume you need a fairly easy, but rewarding project that you can have fun with, while keeping peace in the family.
I can only tell you that I regret letting my little Rambler American get away from me. At the time, I had a Model A with no intention of selling it. However, I met a fellow with enough money to change my mind and the A-bone is gone.
If I had the Rambler today, I'd go with a mildly built 258 and adapt a 5-speed. (I've heard that Ford 5-speed transmissions are almost a bolt-up)
I'd definitely get a different rear end........the original Rambler rear end, with it's tapered axles and weak differential, is junk.
Build a good solid engine, with a mild cam, paying close attention to the breathing and lower end. (A high-pressure oil pump is not necessary, here, just good factory clearances and attention to detail....and a new pump just to ensure dependability)
Once you got it up and running, you could make subtle changes, one at a time, until you are satisfied with it's performance.
The 258s, with some modifications to the exhaust system, like dual headers and dual free-flow mufflers, along with a less restrictive intake and carburetion, really brings these engines to life.
There should be plenty of room to put about any modern six in the car with a minimum of effort. Even Ford and Chevy sixes could be a choice and they may be easier to get parts for.
If I wanted a lot of power, I'd consider the 300 Ford , or 292 Chevy sixes.
Just some thoughts from an old fart, who let too many good ones get away.
