When your mechanic friend said there is a chance the repairs may work, is he saying once the engine is disassembled that more problems may become apparent, thus taking more $ to repair?
How many hours on the engine? If it is a high hour engine I would just replace it because even with the mentioned work done it may not be long until you need valve and or carburetor work.
If you can't do the internal engine repairs yourself it usually makes better economic sense to replace the engine.
If it is a low hours engine and you have a good mechanic, I'd take a chance on the $200 repair.
If you want people to notice your faults, start giving advice.