High RPM Backfire when fully warmed

Okay, so I guess there’s my issue. Not sure on installed height. I just had bought Hughes locks and retainers and those 901 springs and gave them to the machine shop to slap them together. So I’m probably going to have to pull the heads it’s crazy that I been running the car like this for a while now.

Another question Hughes 1110 springs would be the cure for this? How much more lift would these handle just in case later down the road I install a hotter camshaft?
All the info on the Hughes spring.

https://www.hughesengines.com/Index...bnVt&level1=VmFsdmUgU3ByaW5ncw==&partid=35162

Personally I’d throw jet in it first just rule that out. The temperature variation still has me worried. Why would it float the valves hot but not do it when cold? Seems like if the spring looses control of the valve it’ll do it at any temperature.