DT 125 Cylinder head and piston rings questions

[Glynn123]

Last weekend I got the Facebook marketplace steal of the year, a nearly brand new DTR engine with kickstart, carb, pv servo and a few other little goodies thrown in. Drove the 200 mile round trip to get it and was amazed what was under the dust, this things never been stripped or broken apart in any way, the carburetors litterally new and unseized too! Shame I've just got my Polini 32 working well.
I pulled the barrel off leaving the head intact to check ring gaps and head type, rings we're stuck from plug being out and slight moisture, but once freed the piston and bore looked brand new, no scores at all.
Ring gaps sitting at 19 thou, as far as I'm aware this is out of spec, what's the best rings out there to fit a standard bore Yamaha piston? And is there really a great power loss with the ridged cylinder head? (Think the engines an 03?) I could strip the unrestricted head off my old engine which is already skimmed but I don't really want to disturb the head gasket if there's not too much power loss?
Cheers

[Calum]

Something like 80% of the power is made at the head.

So yes, a restrictive head will dramatically affect the power.

[Glynn123]

I'm more thinking of how resitrictive is this head in comparison to the other DT ones?

[Calum]

@Glynn123 Yeah, pretty restrictive. People say how noticeable it is.

[DanRacing]

@Glynn123 You said in my other post about me porting your cylinder, I advise you to send me the head aswell to get it machined to spec and derestrict it, as for rings, can't beat yamaha original ones for stock yamaha piston.