Is it possible to do a interior thread in acme? I'm talking cutting a 5 start 3/8-5 1 turn per inch. I need to do about 20 pieces.1"square delrin. Is it possible in lazyturn or should I farm this out?

Is it possible to do a interior thread in acme?

YES

Is it possible in lazyturn

NO as LT is for doing profiles and dosen't provide code for threading. You need to use the wizard.

Have look at Threading on the Lathe - Mach 3 write up  as  multi start treading is talked about. You really need a good cnc lathe system.
You can use alternate flank cutting to cut acme threads, 5 start ....i would not even attempt it here on the outside yet alone on the inside.

Frankly farm it out unless you have tested and done that kind of work.

FWIW,

RICH