I swapped in from a 6.5 single to a 5 something(I never counted the teeth) high two speed in my ‘54 630 with a 503. Milled the head .092”, has adequate power at 5200’ elevation.

Ed
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Last edited by EdPruss; 01/24/2025 1:41 AM.
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
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