Mike, sorry, i would say ...'lrsd' is probably long shaft - remote - electric start - whatever 'd' stands for
dlune, comparing the 20 and 25 specs in the shop manual:
the 25 gets 25hp at 5500rpm +-500, max torque is 26ft-lb at 4000rpm, and fuel consumption is 239g/psh.
the 20 gets 20hp at 5000rpm +-500, max torque is 25.7ft-lb at 3000rpm, and fuel consumption is 214gpsh.
...this should help the discussion, i don't have any further comments at this point, i'll think about it. As Mike says, carb and camshaft likely changed the power curves, probably ign. is different too?, which resulted in these specs. in general, i see that the 20 gets it done at lower rpm, so in theory it should last longer then the 25, but they are both gonna last forever, so it doesn't matter.
re: repair. it looks like you disconnect shift shaft down low, undo the rubber mounts, undo those bolts, and depending how much wiggle room you get, you may need to remove gearcase, or extension case to get it to drop down off the upper shift shaft? you're lucky it's not on the boat, that would cause you another hour or two. btw, i haven't actually done this on this motor, but that would be my approach to start. I don't want to be responsible though if it gets more involved
Let us know how it goes.
i wouldn't change the rubber unless there is damage. i would replace all bushings and sleeves that you disturb, wash up the parts, and apply the right grease, and torque on re-install.