In my experience the Passon kid has a bad attitude.
That alone, IMO, would make me steer clear of dealing with them.
When a business says they are looking for cores that you have, and they have a core you can use, you don't get all cocky and snide, pulling an attitude trip, when trying to buy the cores you need.
You just say "No we need this core to rebuild for our own".
I can handle "no", but not a holier than thou attitude.
Now Brewer's gets any extra older core 4 speed stuff I have, when I have it.
As far as an after market manual transmission, KEISLER would be my choice, because there are no other sensible choices offered.
Mark.