I have a '96 truck vortec 350 in my '68 that is stock except for a performer RPM manifold. Before I put the manifold on the motor, I was checking out the thermostat by-pass hole in the block near where the water pump bolts on. I ran a plastic straw from a WD-40 can up through there, and it wouldn't go past the surface of the block. The water jacket of the head has a hole that would match up with this hole, but evidently the head gasket does not have a hole there. I knew that I had to have some kind of by-pass so that coolant would circulate in the block before it got hot enough for the thermostat to open, so I drilled a 1/4" hole in the thermostat flange. This worked fine in warm weather, but now my problem is that in cold weather, a 30 minute drive won't even get the engine up to even 160 degrees (engine runs poorly & no heat !) because all the water in the radiator is circulating all of the time. I don't know what kind of by-pass was used with the factory set up, some kind of hose, I guess. Does anyone have any idea of how to make a bypass around the thermostat ? I don't really want to pull the head and change the head gasket. Thanks, Ron.