heater core

88 BFN.
Mine has what i believe to be an aftermarket but almost seems like it could be a factory optioned heater mounted in front of the driver. The hoses have been disconnected and i suspect someone didn't winterize it in the past and never hooked it back up.

question being, I cannot track down a new heater core. my radiator guy can't get one that is the same dimensions. it lists for a 70s ford f100. but is NLA and has no superseded part numbers.
the heater plenum box has a label that says Master mark Inc. lake worth fl. Model no. H-1 serial 89525.
core measures 6"x6" with the feeds both on same side.
plenum box measure 7.5" x 6.5" x12"

The part number i get when i look up the core is 91577 in Balkamp catalogue

Only option i have found is I can buy a 6" x 9" core and do some fabrication work to the box but i would rather not.
Anyone found a replacement for theirs?

yes, the problem is the f100 core now comes up as its newer larger counterpart on anything that is current. so i'm guessing they made a upgrade at some point that fit the f100 plenum.
the only place i can find the smaller 6x6 core(not including tanks) is if i look in the older out datedd books. but any tries at cross referencing the number from the old book gets me nowhere.

Tony,
Have you looked into replacing the heater? Sometimes a part can be more expensive than the complete unit. You'd get a new blower too!

I found a place on the internet that had cores,and there is more than one due to the angles of the pipes,but like Pete says a new heater might be better they were 190 each! Mid fifty.com