I just finished putting A C cores in my Lancair 235.

Tried the junk yard trip and spent about $100 before I decided that was not a
good idea when you are cooling a 60 t0 70 thousand dollar airplane.

Buy new cores for about $125.oo each and have a pro weld the new fittings
into them.

One problem with old cores is that they are full of refrigeration oil and
this makes them hard to weld properly.

Hank H. LNC 235 Rotary - flying