There are Three Differnt Injection Pumps for the 5.7 Diesel..
The 78-80 Pencil Injection pump.. This pump will only work right on these early Models with Pencil Injectors..
The 80 Poppet Injection pump.. This pump was made only in 80 but will however work ok with 81-85 engines.
The 81-85 Pump.. This pump has a cold advance solinoid that advances the timing 2 degrees when cold..but it will work with the late 80 poppet engine.
Getting an exact replacement always assures correct operation..
A Stanadyne/Roosta Master facility can also turn the fuel up in your pump..which gets more fuel to the injectors..but it really isnt a big deal without bigger injectors.
Advancing Timing degree (the width of the mark is about a degree) or so boost performance a bit...But be careful!