differences between newer and older 350's

[86mk7]

Does anybody know the differences between 350's.

Mainly a 91 1500 4x4 350 and a 99 4x4 350

I know the fuel system and what not is different. But what about the short blocks.

 

[Ceejkay]

91 has Flat lifters, 2-bolt main, block #638, head #191, 193, valve cover bolts through center of cover. 99 has Roller cam, 2-bolt main, block #880, head #906, valve cover bolts thru center of cover, plastic timing cover with crank sensor. Vortec

 

[retorq]

Vortec blocks don't have an internal coolant bypass built into the passengers side head, that's the biggest difference, you HAVE to account for that. Also the crank and timing setup on the newer block is a bit different to account for that crank sensor.