manifold vaccum for vaccum advance ?'s

You failed to mention(unless I missed it somewhere) if it's an electronic distributor or points. I'll assume it is electronic since nobody "upgrades" to points. Popping from the exhaust sounds like combustion in the exhaust system. Probably not caused by the vacuum advance since it only adds advance to the timing & popping in the exh would be more likely a retarded timing situation. Not likely in this case. What type of ECU are you using? Is it compatable with the dist or is it functioning properly? I'd get a hold of a dwell meter & check the dwell on it. If it is too severe it will cause the popping you describe & cause the coil to get hot. I'd also make sure your not confusing the popping with a misfire. That too would cause the exhaust to become overly rich & then combustion could start in the exhaust. Do a power balance test on it to be sure. Also check you manifold vacuum with a gauge & see if it's steady & how many inches @ idle. Post your results here & we'll go from there. Good luck.