We to have an "M" code 69 Mach 1.
Our heater hoses are as follows...
The upper hose on the firewall goes to the water pump. (the lower of the two pump connections) and the lower firewall connection goes to the Intake manifold on top by the radiator hose.
The uppermost (of the small) water pump connections is connected to the front of the intake manifold at the thermostat cover with a short 90 degree (angle) hose.
Hope this helps.
PS. Is your factory intake cast iron or aluminum?
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