We now have two styles of Heater Cores for the popular application of 65-66 (all models) and 67-68 (without Air Conditioning only) Mustangs.
The original part number IN9022 was changed to an aluminum replacement design by the original manufacturer. This is a nice heater core, but we have found that in order to install these in some heater cases/boxes, it may be necessary to slightly file the two holes in the case where the heater core tubes come out. The tubes may be just a bit too close together, so the holes in the case may have to be filed to accommodate perfect fitment.
We also just got a new heater core IN8304 that is just like the original copper design and fits the case with no modifications.