Welcome to OCC.
Several things need be considered when rebuilding an engine:
Are you going to have to rebore it oversize? that can only be determined AFTER tear down and precision measurement and inspection of the bore for scoring, egg shaping and taper.
Then on to the crankshaft as to the condition of it as to the journals and connecting rods.
As well as other things like valves/seats, camshaft condition, governor etc. Etc.
Your friend "Butch" prolly knows that if he is an experienced mechanic/rebuilder.
But if he isn't, you might wind up with worse that you have now.
A quick search of your part numbers for the standard rings, produced many hits.
One on ebay, listing number # 174897833124
Also Hastings piston rings makes just about every ring known to man if you want to personally contact them or search their site.
They do not sell direct to the customer, but armed the correct part number recommended by them, your local auto parts can order them for you. BTDT.
I didn't go any farther, as if I can do it, so can you.
And it is a moot point, as I stated previously, you do not know the actual size you will really need till you access the condition of the engine cylinders.
One does not go to a drug store and start purchasing pills till you know what your problems are.
All that said it appears your model engine was made for a number of manufacture's of equipment, just not cub cadet specific.
Remember, today we have google and other internet resources that I didn't have back in the 1960's and succeeding years.
Good luck!
