Within reasonable limits, fuel economy has more to do with weight and aerodynamics than with the engine. Once you get to the engine pumping losses and proper gearing to match the torque curve of the engine then come into play. I would expect that the
SBC would have less pumping losses than the beloved old studbuster six.

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2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

Annoy a Liberal, Read the Constitution

Agree. SBC would be the "correct" choice, but the SBF was also a very efficient engine--at least in mass air flow, individual, sequential injection form.

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags

I had a buddy who had about a 68 vette and he said it was pretty unreliable and the motor was nigh onto impossible to work on, so this may have been a factor in this swap.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Being a Studebaker owner, you might be biased.....

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags

I'd never put the study motor in a vette....now a 617 turbo? ...possibly.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

You afraid of tarnishing the Studie?

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags