RE: knocking Saito
Don:
Given reasonable treatment, it's just about impossible to wear a Saito out. Prolonged running with preignition and/or detonation (not the same thing) can damage the rear crank bearing, and eventually loosen the rod fit on the crank pin. Looking in the back of the case if all you see is oil squeezing out of the rod bearing it's OK. If you see an open gap inside the big end of the rod, replace it. I can't say I've ever heard a rod knock in a Saito, just too much other noise.
High or low compression? With the rocker cover off, look at the top of the cylinder around the valve spring. If you do not see a brass ring it's high compression. The cylinder fins - if they are too big to get the cam cover out without pulling the cylinder, it's high compression. These both show it's the ABC version instead of the later AAC engine. Actually has a choke, probably high compression.
The early AAC engines were also high compression, so lack of the ABC cylinder does not mean your engine is low compression, but there were very few HC engines with the AAC cylinder.
The 18x6 prop might be a little much, as Jim said, it's right on the high end of the permissible range.
Pictures:
1) Comparison of ABC and AAC spring pockets, AAC on the left.
2) Cylinder fins over cam box, ABC
3) Smaller fins, AAC.
Bill.