A few test you can preform yourself:
1
Compression test. Will let you know if your head gasket,valves and valve guides are ok.
2
Leakdown test with cda. If air comes out of the exh with the exh valve in the closed position you may have a burned valve or a bent exh valve stem. Rotate engine by hand and inject cda into each cylinder. When I did mine last month I also had the oil drain plug removed, If cda had come from there it wld have been a possible piston ring failure
3
I am told that the bottom end of these engines are very very tough, and unless it has been abused in some way it should be good.
Good luck with this.