Dale, a leakdown test will only tell you about the rings, not the head gasket or head.
A compression test might give you some meaningful information. Probably would. The question is still, where can oil and water cross in that model engine--except the head/gasket. If there's no place else, you need to pull the head.
If there was oil in the coolant some time ago, and then things seemed OK for a while, but it is back again? That's a sign of a warped head or a crack, that heats up under use and allows the oil/water connection only after the engine has gotten nice and hot, and the warp (or crack) expands.
An engine or radiator shop should also be able to rent/loan/sell you tools to check this out at the heat exchanger. You can do a dye test for exhaust gas in the coolant, or excess pressure (meter attached instead of pressure cap) in the system, both signs of the cooling system being "connected" into the cylinders, which it should be. If the problem is only between the oil and coolant, not into the cylinders, that would be meaningless though.
A good mechanic, or engine shop, should be able to give you diagnostic information locally. A decent engine manual should also have diagnostic troubleshooting charts in it, for a relatively objective and expert opinion and process.