If you check your injector pump's label plate, I think. It'll show that the maximum governed rpm is 2400rpm. This is usually designed to be 115% or so of the WOT (under load) rpm. So, if you are clean on the bottom and propped and geared as I'd expect, I'd guess you'll see 2000rpm to 2100 rpm as a WOT (under load) rpm.
I think you should get up to this rpm cleanly or with only a little grey (not blue and not clouds of white) in the smoke. If you see a lot of dark smoke, barring some engine problem, you might be over propped and might want to note the rpm before it gets really dirty as your WOT limit.
The maximum sustained cruise rpm is usually 80% or 85% of this number. So, I wouldnt hesitate to cruise it at 1650rpm to 1750rpm or whatever you 80% number is, all day long. Even 85% would likely be fine if runs clean and smooth.
It doesn't really make sense to cruise a diesel at less than roughly the maximum torque per stroke. On this type of engine that is usually a wide band from 1200-1300rpm to 1500rpm-1600rpm. Looking at the low side of that, that many likely much of a limit.
I've got torque/hp performance curves for many of the classic perkins engines, but ai can't find the one for yours for the life of me. Sorry!