Will a 403 w/THM easily swap into a '56 98 to replace a dead 324?
How about other SB and BBs with their trannies, from 60s and 70s?

 

Simple answer; it will fit. I would recommend if you go this route to also install a turbo 350 along with it. Or a 455 with a turbo 400 will work as well. Takes about an equal amount of work in either case. You will have to fabricate both front and rear motor mounts. change the lower radiator connection to the passenger side. rework the driveline. The easier solution if you want to keep it stock is rebuild what you have.

I installed a 455 and a turbo 400 in my 57 and posted the build thread on here

link to my photobucket account http://s372.photobucket.com/albums/oo169/citcapp/

I have a lot of detail on the swap if your interested pm me