Just started with the same Pump and Fuel system changes on the '74' C-120.
It's also nearly up to 5 hours running since I fully rebuilt the Re-bored engine with the re-ground Crank.
Wanted to check for the amount of cast iron dust in the sump while I drained the oil, so I 'Jacked up' the front end and got most of the oil out.
I then put a blast of air down through the Pump aperture to get most of the residue to the back of the Sump/Pan, followed by a small amount of clean oil and left to drain again.
Just out of curiosity, I thought I'd have a look inside to check how clean it was with my handy 'Scope on a Rope'-
All looked fine and took a screen shot of the Con Rod end, Cap/bolt and the Oil Way for the Crank journal . Minimum focusing distance is about 8 cm-
Not the best image copy, but a handy piece of cheap gear. Just the Drain Tap to fit and she's good to go for hard run.