I did a 235/PowerGlide to 350/350 conversion in my chevy styleline 1950 so I know where and how to fix crossmembers and engine mounts. That time I used Walton Fabrication. Was easy as heck.
The problem today is my 4 speed is really difficult to change gears byt it works. And I have the spicer PTO with two output shafts. It works really well too. So I am struggeling.
Keep original manual gearbox and still have a E-brake that works perfect. And just change engine to a V8. If I decide to swap all out I have to convert to and electric winch and electric power the hoist. And have to try to fit the E-brake drum and that with a TH400 ... don't know if this is a good choice.
Well well, this year busy fixing my Galaxie 59 into running condition. So this will have to wait anyhow until next winter.