The pump is exactly the same from 80 to 89 for certain.
I actually disassembled both pumps and used the best of both. Cover from one, rotor from the other, shaft from the other and so on to make the best out of all of them.
Only difference is that the 500 has a brand name on it and looks like the holes are CNC'd where as the 81 I used looks like it was drilled by hand :P
So i'd say any newer parts are better than NOS.
Also the gears on the 500 give more flow.
The clutch on the 400-450 and 500's are different slightly. But both bolt on and you can install which ever gears you want to from both generations.
I'd go with the 500.
I'm actually getting another bottom end with a good drive train so i don't have to change the bearing on the output shaft.
And I'm going to steal the clutch and oil pump gears off of that one for the Frank :P
That block has a bad crank but everything else is good and I've already robbed lots of parts from it :P









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