I can rebuild it, I'm not local but have shipped all over the US and Canada no problem. To start with, you'd want a gearset from the newer Neons/PT cruisers which are made from stronger steel and the teeth for 1st and 2nd are wider.

You'll also definitely want an LSD. Night and day difference over stock differential.

Also, where are you getting your transmissions? Used unknown ones from a junkyard? Or are they rebuilt?