Hi Dick! Your problem can be easy and it could be complicated. Flat surfaces, cast iron heads, good threads, and a new plain flat copper gasket might solve it all.

The new fiber gaskets has been reported to break more often than the old asbestos gaskets. Something starts to break down the edge of the gasket and soon it blows through. A flaw with the new fiber gaskets is that they either have copper foil just on one side or not at all.

Old asbestos gaskets where was copper foiled on both sides and at the edge. That made them also reusable, something that the new gaskets are not as they stick to the surface and tears at disassembly.

My advice is to avoid the copper gaskets on the market that has a ridge around the circumference and head bolt holes because the head is not that ridgid. The head will bow between holes! And that goes both for iron and aluminium heads. The bead is too high so it is too much material to crunch and the gasket will never be flat. In reality, a bead not thicker or higher than a strong sewing thread is totally sufficient to boost clamping pressure.

The cast iron has a tendency to shift and move, many times material is pulled up by the bolts and sinking at the hot exhaust valve, so a light skimming of both head and cylinder surfaces is recommended. Oil seeping is a sure sign that there is something that needs to be attended to.

Your studs may have stretched or cylinder threads gone bad. Studs is kinder to the cylinder threads than bolts and in theory the clamping force is higher than with bolts of the same dimension. The thin studs Indian used was dimensionally right for the torque the heads needs to be tightened to, but of poor material (and mechanics without proper tools). The factory changed to thicker bolts too short for the dimension so they never stretch, only rip threads out of the cylinders.

Copper gasket with an aluminium head might not work that good as one might expect. Aluminium expands and contracts more and much faster than iron and those shearing forces needs to be absorbed in the gasket, so a fiber gasket is better in that case or the heads might start to wander. Or a modern multi layer stainless steel gasket perhaps, but just yet not available for the flathead Indian...

A fact is that the head is always hotter than the cylinder, even in a flathead! Heat is always transfered from the hot side to the cold side and we don't want the cylinder hotter than neccessary. A good thing is that the heat transfer between the head and cylinder is much less than many is believing, the gap in the parting line is a very effective in arresting the energy (with a head gasket there is 2 gaps). So the gasket material is not crucial for the temperature in the engine, and it is the material properties that is important in order to keep the lid tight, together with clamping force of course.