If you want data on 292 mileage, I can help.
My 292 L6, bored .30-over w/Badger pistons, 8:1 compression, Crane 260H cam, GM HEI, Oversize intake valves [1.84''], Offy 5416 intake, Clifford headers, Edelbrock 1404 [500 CFM] 4 Bbl, in a '68 Chevy C/10 Stepside body, w/SM465, 3.73:1 Corp 12-Bolt Posi rear, and 235/85/R16LTs all around, gets about 10 MPG. I have a heavy foot.

I/I #4101
'71 GMC Jimmy 350, sm465, np205,3.73 posi.
'68 C/10 Stepside 292 (.030 over) Offy Intake, 500 CFM AFB,Clif headers, sm465, 3.73 posi.
'67 K/10 454 project.
'72 K/5 rolling frame project.