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Franklin 90 is a good engine... just won't last as long as a Continental.  Nothing wrong with that,  it will give you plenty of warning as the rings and valves seem to be the first to go.  Just do regular compression checks. 

I have a Franklin 85hp (which is just the 75HP spun faster) that has 1300 hrs on it and has been topped 3 times without spliting the bottom end. 

Also, wood props ONLY!  Metal props are not approved on the 90hp for sure (but also on the 75 /85 I think).  The crank is lighter and will eventually break.

I have flown the Sensenich  -54 prop on a Franklin 90 and found it a little high reving, more like a climb prop.  I think I remember that -54 inches is the maximum pitch for that TC.  Talked with one of the old prop guys Sensenich who told me that there is a manufacturing "plus/minus" on pitch and that if requested, he could make one to the high limit which would be closer to a mid range pitch.

Just a personal observation...  such a clean airframe and wide speed envelope... I have seen 3 different props on the Franklin 90 that would all overspeed in level flight even up at 9500'.  I am not sure there is any (fixed pitch) prop that would not do so.  I do know that years ago 1 (or more) Cadet, probably with 75hp, flew off the end of the runway in ground effect.  I expect it had a high pitch prop and may not have made the minimum static RPM on the ground run.