[packrat5]

You are going to get a lot of "expert" help on this. Okay, first, your MANUAL trans will bolt to a y-block bell housing. However, your trans is a little wimpy so try to find a later one. The input splines were changed over the years, simply use the appropriate clutch disc. Your existing radiator can be used by blocking off one upper, and one lower hole with a soldered on piece of brass plate. Your existing radiator is probably junk, or close to it, so just source a new one. 54-56 radiators fit. The clutch linkage from a 54-56 is supposed to fit, but it didn't fit on my 53 Ford. Could it be made to fit? yes, but I would prefer doing a hydraulic set-up. Use a 56 as they are made to clear a left side exhaust pipe for duals. All y-block starters are the same, 54-55 are 6-volt. Oil pan. Why does no one realize that the y-block oil pump is on the OUTSIDE of the engine, and you can modify the pan any way you want without affecting anything but the pan, and the pick-up tube? T-bird and truck oil pans will work, but not perfectly, it depends on how you mount the engine. Better to modify a passenger car pan to suit your needs. Tie rod clearance is the main issue here. When it comes to the mounts figure out everything else first, so you don't have to re-modify everything to fit your mounting setup. Get some expert advise from someone like Butches Cool Stuff, instead of listening to "water cooler" advise, or gossip from a chatroom, as once done wrong, everything else will be wrong too. This is a relatively simple swap, and once you have done it, (hopefully properly) you will understand.
You know, and I hate saying it, but a chey conversion is easier to do , and you can buy a new in the box engine for barely 5K, which is less than doing a rebuild on a y-block. Easier, less money, and more power.
Also a Mopar 318-360 is a center sump oil pan engine like your flathead, and that is doable too, but more expensive. Now THAT could possibly be cool.
BUT with both of these engines, you will have to deal with a trans swap, or an adapter setup, which can get expensive.
A Ford Windsor engine can be done also, and that could possibly be the easiest of all. Again Butches Cool Stuff has a bolt in conversion. Check it out.