$175 sounds a little steep unless it has a good tank with it. I have an RD-12. It is near identical to my 1954 RD-15A (and 1954 Evinrude 25 HP) except like an RD-11, it has no provision for connections for the usual Johnson remote controls. But if you can be happy with just tiller control, these are a nice (but loud up close) motor. BTW the white stuff apparently is oxidation of the aluminum, I have found it on all 5 of the RDs that I have. 4 of the 5 run good. It does not look pretty but it can mostly be cleaned off by wiping with oil. I think that 88 PSI may not be any problem on a motor that has not run in a long time.
I have a 1956 split cowl 30HP electric start. Much quicker to remove the cowl. It is the same dimensions, weight as the previous year’s 25 HP. Definitely heavier, many more add-ons and it is quieter. Haven’t tried it on the boat yet, but afterwards I may stick to the older, louder, lighter, simpler and easier to handle RDs that have provision for remote controls.