According to the "GMC" Casting code 2135412 in your picture, your engine is a GMC 270 per this GMC resource document. That would account for the difference in the accelerator bellcrank as compared to your other pic from a Chevrolet FAM. You will definitely need to modify/fabricate the needed rod to connect your pedal to that bell crank.

I don't know of any parts immediately available at the moment, but when I get a chance I can check and see what might be out there.

Clarification question: Is your 1954 3800 Panel a Chevy or GMC??? headscratch Maybe post some pics of the truck so we know and can try and help more. wink

~ Dan
1951 Chevy 3 window 3100
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"My Grandpa Carl's Truck and How it Became Mine"
1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver)
US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)