Driveshaft length charts are nuts

the car doesn't have a driveshaft so where do I measure from? The endish, kinda of the transmission, the driveshaft doesn't go all the way and contact the tailshaft.

To where? eyeball the center of where the u -joints should be ??

Under a car with no driveshaft seems to be a lot eyeballing
This is from Cass’s (Doctor Diff) website. It’ll give you an idea what to look for in a OEM driveshaft.

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