Heater core upgrade possible at all?

[Leah and David Mueller]

The 4kq series seems to have very small heater core, something like the old
vw rabbits.  Is there another heater core besides the stock size (or wiil a
new heater core bring more warmth as well) that will fit and provide more
heat transfer?  I searched the archives so I suspect this can't be done, but
I would like to know for sure.

Thanks,
David   1986 4kq