73 Front drive shaft question

[Dads69C10]

I need help.. My 73 blazer is missing the front drive shaft and i found a guy nearby with a ton of parts. I asked him if he had a front drive shaft for a 73 K5 he said yes and asked me the following..

sure do. I need some specs from you though. Is it the type that has a flat flange on the t-case and uses 3/8" bolts to mount, or the type that uses 5/16" NF threads to mount?

now he may as well be speaking chinese to me, so can somebody help me out. thanks

J