Good question, my riser gaskets and turbulators, (phonetic) were bad when i bought the boat. I havent pulled the manifolds yet, there GIL's I believe. I agree with what your thinking my thoughts as well....I was going to tear the top end off this winter and look through it....thought about changing the heads....if the last mechanic was right that used a stethascope, ignoring a rebuild could get really expensive. I've seen some good reviews on Owens Racing Engines here in Houston after researching the forum...saw one bad review that was related to taking forever to get the engine back. Owens suggested changing the cam to a different type...I don't remember if it was a roller or not...said the cam was about $300 and the lifters about $500, substantially higher than stock...if I went with the 500hp - 525hp for a stroker build that type of cam would be used. The stroker was the max the shop suggested on that engine for dependability and longevity.

Regarding hours....I have no idea...there is not an hour meter on the boat....If Dave I bought the boat from is reading...feel free to jump in....I'm not sure if he got a quote from the previous owner...seems like the guy he bought the boat from had 600hp in it, then dropped the mag in the boat when he sold it, I may be wrong but thats my best recollection.

Sounds like the best thing to do is get the thing out and apart. Do some basic inspections yourself.

Check:B
Bearings for wear
Look at piston skirts
look at cylinders

You may need to only ring and bearing the things and spend your money on a good cam, lifter, intake. If you have Gill exhaust now your good to go.