I'll sum up my feelings about the Stinson in one phrase: wonderful airplane...absolutely rotten motor. About the only thing a Franklin is good for is airboat motors and scrap metal.
That having been said, there are at least two STC's that allow the addition of a 0-470 (230 HP). The 108 is a nice flying A/C with almost full roll authority through the stall and excellent pitch stability. Out of 15 different taildraggers I've flown, It's the easiest to wheel land. If I recall correctly, half flaps, 1500 RPM and trimmed for 75MPH. Just let it come down and hit the runway. It rolls on with no forward pressure required. If you buy an earlier mark, make sure the baggage compartment wasn't illegally added, many were.
Nothing special to be cognizant of beyond the usual 55 year old rag and tube airplane issues. (Univair is gonna cost you man....)Some have been metalized. (Heavier and slower) That stuff about the Franklin isn't hyperbole either. Don't even think of flying one unless your life insurance is up to date and your affairs are in order. Lastly, if you buy one, get a thorough checkout from an owner/CFI and make SURE you have shoulder harnesses. (Good advice for ANY antique taildragger)
Good Luck!