Hi again wazzbat, and welcome back to the forum.
You have posed some good questions here...I'll do my best to give you some answers.
If you intend to restore the Model 33 down the track and keep it all original...then sourcing a replacement Kirby -Tecumseh engine would be the way to go...repairing your engine could be difficult because of shortage of over-size parts that would be required in case you have to re-bore the cylinder....Until you pull it down, you won't know what damage has been done...
2nd option is to replace the Kirby with an older 3 HP Briggs (as used on the Model 45) but you would lose originality.
Selling it as is, would be another option.
As you say, the Model 33 is getting long in the tooth as a working machine and a Model 45 (all parts still available) is in my opinion a better option long term.
Now to the SB Model 45 versus Rover 45...some say the original Scotties have a better build quality than the Rover; but never having owned a Rover, I can't comment other than to say that some smaller items were changed when Rover took over SB...the double race engine shaft bearings for example.
The Model 45 was first introduced in 1968 and featured a solid engine deck...whereas the later Scotties (my model) have twin rails (as does the Rover). Some say the solid deck is better, less prone to cracking due to vibration...mine however, is still fine with no cracks.
I prefer the later 70's models myself.
I think that $500 for a 7 year old Rover 45 is a good buy, but before you do decide to purchase...
please post the whole string of numbers on the Briggs cowling (or elsewhere) so that we can determine the exact age of the engine and give us a rough idea of the age of the machine. Don't forget these machines were $1800+ when new.
Clutch problems are a relatively easy fix and we can step you through the repair procedure, if necessary.
Looking forward to seeing some pics if you can take some on the weekend.
