67 Engine Tower(mount) differences

[Dan 67 Chevy LWB]

I have 67 Chevy that originally had a I-6 with standard trans. About 15 years ago pulled the I-6 & trans in favor of a small block and TH400 trans. I don't remember exactly what i did, but looks like i just opened up the holes on the engine tower to bolt the small block in. I also just modified (welded mount) to stock trans crossmember.

I'm now planning on going to a big block and either staying with the TH400 or putting in a Overdrive trans(i have one i think is 700r4, but have to verify it).l

So what i'm looking for is the difference between the different Engine tower(motor mounts) and trans crossmembers. Is that a site that show and explains the differences. Or a supplier that shows the different mounts. Also do you know who sells the big block towers?

Thanks