You can be rest assured that the I6 will take even more space than a 350. I have a SBF in my '31 and the firewall is back 5.5 inches with a Bitchin' bell cover to use up even more toe space. I had originally wanted a 5 speed but that idea had to be scrapped for a C4 and a modified brake pedal. But, with that said, it really sounds like a fun idea - with no belly button engine such as SBC, but would rather hear that the bigger GMC (270cid?) engine was to be used.