Do it right, remove all the AC stuff and put in a non-AC box. It will look like crap and be ten times more difficult than doing it the "right" way.
They don't seem to be as effective because the STANDARD heater blower motor was not the same as the AC AND the HD heater options, (which do move more air) which was the base heater setup, with the AC blower motor and a vent tube added. (you can run the AC blower motor on the standard box by changing the squirrel cage and either leave the vent open to atmosphere or making a small filter for it)
Again, the effective difference was all in the fan/motor, nothing else. A HD heater setup works just as good at moving air as the AC setups.