You might want to mount the HEI module on a piece of 1/8" thick alum say 2"x2" with some heatshink compound under the module... then bolt that to the fender.. or at least use heatsink compound under the module and ensure you have full contact between the HEI base and the fender surface. Hot spots can cause issues.

Keep a spare module in the glove box just in case while your shaking the bugs out.
51 GMC 4.2 turbo
Can't solved today's problems using the same technology/thinking that created them