Water Pump Bolt Length

[Kilian]

When I removed the water pump from my late 1970s 350, there were three different lengths used. Since there isn't a difference in thickness in the water pump casting, and I don't see much difference in the block, what length is correct?

Four 3/8-16 x 2" bolts?

Thanks!

 

[bucket]

Whichever length is the one that gets you enough thread engagement, plus more to spare. Iirc, the original bolts have around 5/8" of stickout.