Deve,
You wrote "In addition some extra engineering took place since they wanted the thermostat to be bypassed to a small extent on startup before the engine reached its temperature. Lots of guys do this on their 216/235 engines by drilling an 1/8" hole or two in the thermostat."
The Bypass thermostat was designed to circulate coolant through the engine as soon as it was started to prevent hot spots/steam pockets from forming. This was done by allowing coolant to flow through the lower ports in the T-stat into the lower half of the upper t-stat housing and back to the water pump via the Bypass Hose while the engine was cold. As the engine warms up the bypass ports will close and the main port will opened to allow full flow of coolant through the radiator.
The 1/8" holes drilled in normal 216/235 T-stats are there to bleed off any trapped air, not to act as a radiator bypass.
So what changed in the '59-62 engines requiring this Bypass to be added?
Can you give me the casting numbers you and Tim have on your upper housings.
Also confirm the inside top of the upper housing has a machined surface to axcept the top T-stat seal/gasket.
Thanks,
Mike B
