I've never seen a small block with an extra bypass hose, just circulates through the heater.
Here's one.
I had the same problem on my small block with the vortec heads until I added the bypass. I couldn't use the little 90 degree hose and fittings because I already had plumbed the heater into the top of the water pump. The problem has to do with the iron vortec heads that were used on late 90's trucks that requires the bypass. Some used the heater coolant circulation for the bypass because the heater control valve bypassed back to the water pump when the heater coolant flow was closed off.
I think Tramp did his happy dance when he fixed the problem.
Mark
