400 is a steal! Great car.
Some things to search for....the '51-up Chevy's have Bendix brakes, far superior to the Hucks brakes on a '50. If you can find a '54 automatic parts car, you'll be laughin'! The '54 'Glide cars have a 3.55 rear end ratio, much better for cruising than the 4.11's you have now. Swap in the whole rear, brakes, driveshaft and all. The front uprights off the '54 will lower the front end about 1" too. If you are swapping to the better brakes, might as well put the uprights in at the same time!
A stick car would have had a 216 from the factory, but lots can happen in 60+ years. A 216 has the side plate going up into the head, around the plugs, a 235 plate ends at the top of the block.
There is a chance that a pressure-oiled engine has been swapped in. A "dipper" can be identified by the three bolt tin plate just above the oil pan rail, in behind the exhaust pipe. 235's can be either way, 216's are all low pressure. If the 30# gauge pegs when running, it's probably a pressure engine, a Dipper usually has only 15# or so warmed up.
Well, that should give ya a dream list to keep you busy for a while! Have fun with that old Stovebolt.