Question on 5.7L Chevy V8 compression

[nestorpr]

Hi guys! Well, I was finally able to check out my engine but first some background; this is a 1993 Volvo 570SP engine which is a 350 cid Chevy with 275hp. The first trip after I bought the boat I took her out for a short ride and the engine overheated, I'm not sure how long it was run in this condition but could have been anywhere from 1-5 minutes, no alarms went off and it was fortunate I looked at the gauge at that time. Turned off the engine and loud metallic clicks and clangs went off so I thought I must have cracked the heads. Towed back to shore and laid her up for a while. I finally took the time to check the compression out and found the following:

#1-170
#2-165
#3-165
#4-155
#5-135
#6-150
#7-170
#8-175

I was not able to warm up the engine first since I still don't know why it overheated and didn't want to aggravate the condition. However, the Volvo manual says the compression should be between 142-156 and these readings seem high, except for #5 of course.

So what do you guys think, did I crack the heads (I don't think so but am not an expert), did I blow a head gasket, is the engine salvageable without a rebuild? Whether I keep her or not will depend if the engine can be inexpensively repaired or not (will not rebuild it or spend more then $1000 for repairs). Thanks for any help!