Glenn,
I think the British product is Belzona (?). This company developed one of the if not the original epoxies and it is apparently super stuff. I think there is a distributor for it in Calgary. Popular for rugged industrial applications. Regards, Bill
P.S.
Good to see you on the forum.

What do you guys recommend for filling in right-hand bolt and loading/ejection port cutouts (to make a left-handed stock) on a synthetic?

Can you just build a dam with tape, coat it with release agent, and mud it up with acraglass?

Thanks,

Steve