ultimately it shouldn't matter, any place you put it shuts off circulation, here's one I put in a 56 - just watch out for corrosion sitting in the heater core in the summer ..... and see the 57 accessory installation manual

Bill


Moved over to the Passing Lane

"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir
"When we tug a single thing on an old truck, we find it falls off" ~ me
Some TF series details & TF heater pics