rebuilt heater box, weak heat

hello everyone,

My daily driver died so i have been driving my 68 while i search for a replacement. new england winters can get pretty cold so i rebuilt the heater box, but i still dont get much warm air out of it. to provide some technical info about the car, i have a 1990 5.0 swap but converted it back to carburetor using a summit brand weiand warrior knockoff intake. im also running a standard rotation water pump. i purchased a brand new brass heater core from NPDLink, as well as the fitting that goes into the intake with the extension tube on the bottom. i rebuilt my heater box using a gasket kit and contact cement to glue the gaskets to their appropriate areas in the box (and yes, i put gaskets on both sides of the door flaps). when the car is up to running temp, the defroster vents are warm at best, and the vent that blows at your feet is pretty much cold all the time. i have provided a list of links to all the parts i purchased and used hoping someone sees where i went wrong. the car also got a new thermostat last year when i put the motor in, but only put a few hundred miles on it at most.

intake manifold - https://www.summitracing.com/parts/SUM-226030
heater core - https://www.npdlink.com/product/heater-core-oe-style-copper/146337/200457?year=1968
heater core ends - https://www.npdlink.com/product/end-cap-seal-heater-core/103093/200457?year=1968
gasket kit - https://www.npdlink.com/product/gasket-set-heater-box/103210/200457?year=1968
intake fitting - https://www.npdlink.com/product/connection-heater-hose-zinc-dichromate/206393/203317?year=1968
plenum - https://www.npdlink.com/product/heater-plenum/103050/200458?year=1968
defrost hose - https://www.npdlink.com/product/defroster-ducts/178786/200458?year=1968
control cables - https://www.npdlink.com/product/cable-heater-temperature/103098/200459?year=1968

i would like to say yes, but im still going through the shambles of wiring that is in the car, so i have no way of telling because the temp gauge doesnt work.

Noobz347 said:

Ah! That might be a good place to start. Ensure that your t-stat is opening and closing before you dig too deeply into the rest of it.

Any idea how long it's been in there?

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i put a new thermostat in it about 2 years ago, but it only has collectively about 1,000 miles on it. thats why i was ruling it out because i assumed it would still be new enough to be working as it should be.