spark plug reach

[russcc]

When you get the right reach plug for the head thread depth, the right electrode and correct heat range, that's 80% of the battle. Then, either shims, counter boring the top of the thread in the head, or chamfering a thread or 2 out of the combustion chamber to unshroud the plug and prevent pre-ignition is a combination of comprises given the flatheads plug location over the exhaust valve. Some research, especially here on the barn, some machine shop skills, and dial indicator and you can solve the problem