Re: SBC to BBC in a 68
I ran a BBC in my '69 for years with the SB frame mounts and a TH350. However, to do it right, you'll need frame mounts, heater core and cover, different exhaust manifolds/headers, different fan shroud. There are numerous other small parts you'll need, but those are the major ones. The stock brake booster should still work unless you've got tall valve covers. I can't say for sure since my car had manual brakes when I was still running on the SB frame mounts. You've got a PM.
Experience...... It's what you get when you didn't get what you wanted.