The challenge with recommending a source for an OEM driveshaft is the number of options available. For example, American Axle has an incredibly detailed tech library for driveshafts they produced for OEM:
https://www.demandaam.com/technical-...l-of-materials
GM part number 23251121 from 2014+ light trucks is listed as 60.91" from U joint center to center. Following part number 23251121 down the rabbit hole we find it is specifically used in the following models:
2018 Chevrolet Silverado 1500 Custom, LS, LT, WT 4.3L V6 - Flex
2018 GMC Sierra 1500 Base, SLE 4.3L V6 - Flex
2017 Chevrolet Silverado 1500 Custom, LS, LT, WT 4.3L V6 - Flex
2017 GMC Sierra 1500 Base, SLE 4.3L V6 - Flex
2016 Chevrolet Silverado 1500 Custom, LS, LT, WT 4.3L V6 - Flex
2016 GMC Sierra 1500 Base, SLE 4.3L V6 - Flex
2015 Chevrolet Silverado 1500 LS, LT, WT 4.3L V6 - Flex
2015 GMC Sierra 1500 Base, SLE 4.3L V6 - Flex
2014 Chevrolet Silverado 1500 LT, WT 4.3L V6 - Flex
2014 GMC Sierra 1500 Base, SLE 4.3L V6 - Flex
It's an aluminum driveshaft and uses a 1355 U-joint which (I believe) is unique to AAM driveshafts. Dimensions at the U-joint are 1.188" cap diameter and 3.612" across the cap. There are crossover U-joints but there are not many options. Moog 447 is listed as a crossover with one side measuring 1.188" X 3.625" and the other spec'ed at 1.125" X 2.560" which is a common GM size that typically uses a Moog 534-G in a stock application. This joint *should* fit a stock rear yoke for most '76 F cars. As to whether or not it will fit your front yoke, I cannot say.
Maybe there's another part in the AAM list that does not require crossover U-joints?