High RPM Backfire when fully warmed

MOPAROFFICIAL said

The 901 is stock 340 cam spring and
won't work.
What installed height are you at?
1.64 or so?
I like to use 145 lbs or so on the seat and around 300-360 open for up to .500-.550 lift hyd rollers turning 5500-6000 rpm.
Stock reground core?
Yours shouldnt need more than 300-330lbs open.

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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?