78 f250 d44 &d60 lug size???

I'm betting 9/16"
 
They're 1/2-20 thread...even the Dana 60s, but I always change them to 9/16-18. Dorman # 610-278 Application is a 90s model Ford Dana 60. Drill the holes out to 39/64 and tap them in with a hammer.

If your rear axle is the matching Ford axle, then they're both 1/2-20 and I'd probably leave them unless they look crappy. However, if the rears are 9/16-18, I'd change the fronts to match as they are FAR more common.

Any 8 lug wheel will fit the 1/2" studs, you just have to get the right lug nuts. That's the pain in the ass part.
 
I recently swapped to a 2500HD front brake setup on my Silverado 1500 with a 79 Dana 60 up front, so I knocked in some 14mm-1.5 studs to finally have front and rear matching lug nuts :D I also gained much better brakes, better availability of parts, and now the front rotors slide off!
 
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