• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Hammond OT 125CSE for RH84 rev.2 ? A good choice?

No. Hammond tells you this pretty clearly in the specs. They are almost OK when run as 2.5K transformers, but still not all that wonderful.

I would, at minimum, recommend these (they are the same price as what you're already looking at, but a bit heftier):
EDCOR - GXSE15-8-5K

If you need something ASAP, One-Electron makes a nice 5K output transformer, but it's quite a bit more expensive than those Hammonds.