How close to the muffler or cylinder head can I mount the ignition unit? Would 3/4 in clearance be enough ? Worried about heat on the unit.

The unit is potted so is vibration an issue ? do I need to insulate with piece of foam rubber ? Tks

I don't think I would place my IU that close to the exhaust. I don't have any reasons other than common sense would dictate you not do that. Most of the time the Hall sensor pig tail is long enough to place the IU out of harms way.
Yes you do need to mount the unit in foam. Treat it like a Rx or a battery.

Can you make a cooling chamber fo the ignition? It may work if you do that.

No room to make a cooling box. Space is premium in the GP Christen Eagle despite it boxy looking cowl . Thats why I had the ignition battery inside the plane just behind the firewall next to the fuel tank . I was thinking of velcroing the ignition unit to the engine box on the carb side with some foam between for vibration insulation but that may not be enough for isolation . May have to end up placing it insde the plane behind the firewall but then i need to drill out another hole in the firewall for the ignition cables etc.

about 2 years ago there was an issue with heat affecting some electronic ignitions. I would not install it in the cowl at all, drill the holes.

I agree with Excaliber. I had one of those older units and a heat build up and a failed ignition unit assisted in the loss of a plane. Find a way to move the ignition away from the exhaust. Near the engine is not a big problem if you can have some airflow over the unit, but close to the exhaust is not a good idea.

Will locate the ignition unit in a well between the back of cowl and the L/G at the bottom of the fuselage. Its away from the muffler and on the carb side, also open to air flow to get some cooling.