Re: 1951 Elgin 5hp.
They were ok.
Had a bit of trouble with water getting up into the powerhead through the lower crank seal, which trashed all the bearings. I'd replace the seal whether it needs it or not. If it is too late, it is too late.
Had a bit of trouble with shearing all the fins off the impeller.
Had a bit of trouble with corrosion collapsing the bronze water pump cartridge.
Had a bit of trouble with the rubber cuff that attaches the tiller handle coming "unglued".
But if in good condition, they run well and give good service.
EDIT: Oh, one other thing..had a bit of trouble with rusting out of the drive shaft / crankshaft splines.