I'd be more worried about blowing a head gasket or throwing a cast rod. I hope you run 93 octane or better gas with those 670s. I run those heads on a '67 400 in a '67 GTO/LeMans. The 670s are great heads, just high compression with most pistons. Don't revv your engine over 5200, use good gas and you should be OK. Just watch oil pressure and engine temps. Listen for detonation, which sounds like valves rattling.
The 8.2 rear ends that came stock in '67-69 Firebirds or GTOs can only take so much abuse too. Typical failure is twisted axles or broken gears. Taking any car to a dragstrip is an assumed risk. No lifeguard on duty, swim at your own risk. Did I mention to check your U-joints and brakes before flogging at a dragstrip? Ending up in the kitty litter doen't impress the chicks. Ask me how I know. LOL
good luck
robertg
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I could explain all this to the girl at the parts store, but she'd probably call the asylum.
White '67 LeMans 407/TH350/Ford 3.89... RIP
Red '67 LeMans. 407/TH400/Ford 3.25
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