Help with my 2000 YZ426F

Hello! Any help would be great on this. I bought a 2000 yz426f that was completely dismantled after a valve strike on piston. Head was rebuilt by previous owner. Replaced cylinder and piston using instructions ive found online with genuine manual and it ran fine for about 2 hours. New gaskets and torqued to spec. Clutch started slipping while riding then found leak from head gasket and lower gasket was wet. Stopped bike and let it cool. No overflow from top of rad so didn't think it was over heating. Noticed oil was thinner so presumed coolant had got into oil. On dismantling I noticed head bolts were a tad loose. New piston was completely scored down one side and rings were almost welded in on one side. Cylinder scored, looks knackered.

Looks like I've bought a money pit :( what do you guys/gals recommend?

I sent head off today for a skim. Should I do pressure test too? New piston and cylinder.

Worried about wasting a load of cash on this. Any ideas? Am I best sending off to a pro to do?!

did you put oil in it? they have a frame oil tank

Yea I put oil in 1.7ltrs I think in total. There was oil running to head and I cleaned oil filter too

hard to say, its possible that the crank or cases are damaged causing the piston to not be riding square to the bore,

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