A JMOD...for free? Sounds like you are taking it to my shop for me to do for you!!!(but, you arent).
For some of us, doing things for friends gives us more satisfaction than any dollar amount can.
I have done 4 JMOD's...mine, and 3 freind's. I havent received a dime, nor would I accept a dime.
But...I am sure you will find SOMETHING the tranny-man could use...I "needed" some stuff for my car. I never collected a dime for my work, but I ended up with a Hayden tranny cooler, a nice 12" sub/amp/installation kit(used, of course,), and some MSD wires.
The guy who provided the "thump" is heavily into car stereo's. He showed up to have me do a full tune up, JMOD, new front struts, etc...I ended up with some nice stereo components...I knew nothing about sound systems, but installed the goodies myself...and love every minute of it.
My point is, you might be getting a free JMOD...but you might consider finding out what "tranny man" could use....perhaps some yard work? or better yet...shop clean up?
hell, if I were you, I'd spend alot of time at his shop, and learn as much as you possibly can. even try to help with the JMOD. Who knows...one day you might be "pimping" some work for him. If you run across some Mustang boys who want to know why your car BARKS into second gear, and theirs doesnt...send them to your tranny man...let them "pay him"...
Good luck, be sure to thank the guy plenty, and then drive by his shop and let him hear your rears chirp into second...that makes any tranny man happy!