The stock light duty 3-sp was used behind many transplants of the day, including Olds Rocket V8's, Buick nailheads, and Caddy V8s. As long as you're not doing burnouts a lot, it will give a reasonably good life. If you want to avoid cutting on the crossmember, a HD 3-sp would be just the ticket. Totally bolt-in, just some driveshaft mods. You should have a 3.73 rear axle, that really isn't too bad as long as you run tall tires (28" - 29")

I'm of the Option 1 persuasion, you have plenty of places to spend time and money on it without touching the drivetrain.

 

I ran Willard, my 49 for a number of years with a 56 Nailhead Buick thru the stock trans, however fairly early on I found a heavy duty 3 speed and installed it. I had to replace syncros and gears a couple of times in the LD trans. The problems went away with the HD trans install. I would definitely recommend the HD 3 speed behind the sbf.

 

Thanks everyone for the responses. I went through my parts and found some flathead stuff. It's enough to start and at least mock up the engine compartment. So for this build I'm going to put the original flathead back in.

It's going to be a while before I start this one heavy. In the meantime I'm going to put the 60s era stuff I talked about in 64 F-100. That one should be a very fun and simple build.

So I'll keep everyone posted on the 50 via this thread as things happen.