Thanks for the reply. I don't have the twin thermostat mods and I don't have an over heating issue either. In fact just the opposite. I can't seem to get enough heat out of my K5 during the Winter mos. But that's a whole different thread. I replace the w pump 3 yrs ago . The engine is a '91 so I ordered a pump for a '91. When I got it it had a bolt pattern different to the one on the engine. So, I went back and got one for an '84. That one fit. The felpro engine gasket kit I have has 2 different gaskets . I have since gotten a timing cover gasket kit ( for other work that needed to be done) and it also has 2 different gaskets.
I want to order a new pump from Rock Auto but there are at least 3 different Delco part numbers between an '84 and '91. For a '91 their listing says there's 2 different pumps and to verify which one I need . Unfortunately they don't say how.
I just want to get the right one ahead of time.
84 stepside with 3-53T Detroit 5 spd O/D Spicer
88 K5 was 350 TBI now 6.2L with GM3 turbo
84 dually crew cab 350 4spd 2wd
83 K5 6.2 diesel plow truck
98 3500HD 6.5L turbo diesel NV4500 going to be extend cab with 6V-53T, ZF 6spd and Mitchell aux. overdrive
Lots of parts trucks to keep the fleet going