I checked Wallace racing and the 7k3's are comparable to the 6x-4's with the bigger exhaust valves and ~95cc chambers
see: Wallace Head List
Not sure what your budget is, but I'd suggest considering a set of aluminum heads, they come in 72 & 87cc's

I installed 6x-4 heads some time ago on my 400 YT engine and it runs well, but I gave up compression/power. The original heads were 10.75 compression #62 heads, [72cc] and they pinged big time unless I ran race fuel.