SBC or BBC in 1972 K20 Suburban project vehicle?

[kabcpapc]

This was originally posted in the 1967-1972 Suburban forum but got moved to another forum. So here it is again.

I am getting ready to start on a 1972 Chevrolet K20 Suburban project. It has a 350cid with a TH350 automatic trans which is the originalengine/trans. I have been away from the GM camp since 1989 so I need some tutoring to reclaim my memory about GM engines and transmissions. My dad had a 1972 Chevrolet C20 Suburban with the 400 BBC with automatic which I felt sure was a TH400. My prior memory told me that SBC had the TH350 and the BBC had the TH400. I was contemplating installing a BBC with a TH400 in my K20. In the various threads I have read on the site, a lot of guys reported inadequate firewall clearance when installing a BBC and they had to move the engine forward or cut out more space on the firewall. They also said they reused the SBC motor mounts. Now my dad's 'burb had plenty of firewall clearance with his BBC. According to what I have found out, the BBC used different motor mounts than the SBC.

So to make a long story short, can you install a BBC with a TH400 in a K20 without cutting on the firewall by using the motor mounts that was used on the C20 BBC?

[Infanti]

The issue with these trucks is that the 4X4,s never came with BB.Only SB.The engine is set back on 4X4 trucks compared with 2 wheel drive trucks.
2 wheel trucks had both the SB or BB mounted in the same place.This is why if you mount a BB in your 4X4 it will have firewall clearence issues.You can mount the engine forward but then you have to modify your drive shafts.
You could also use a 700 transmission which is longer than a 400. This way you could leave your transfer case in the stock location and it would move your engine foward giving you more firewall clearence. Hope this makes sence.
Anyone with more info feel free to jump in if i am wrong.
Gerry