My dad is really hard on his bike too. Anything we could do to get a big bore kit to be reliable? O ring the head? Idk never worked on a 4 poke.

I do not know if there is enough room for a rubber o-ring on the big bore setup.  On a four stroke head it would require an o-ring on both sides of the head gasket and would require a single ply head gasket.  Now we can hold the compression but now there may be coolant or oil leaks because of the single ply head gasket.   Sometimes we install a very small diameter wire type 0-ring but it is usually a one time deal on aluminum heads and cylinders.  Next time you remove the head you have to mill the head or cylinder so that the wire has a new surface to embed itself into.