First, when you had the job performed at the transmission shop, what was the warranty that was written on your bill of sale for the services performed? If it was only a verbal warranty, he may claim he never said that. Most sales receipts will have all warranty information clearly printed on them. A transmission place, not associated with FORD, can not force FORD to cover any work that they did not perform.
Second, when you brought it back to them after four days, did they offer to look at it and try to fix it, or did they say no warranty??? You must give them a chance to repair their work, not just ask for your money back under this situation.
Third, if FORD has documented that the transmission was faulty or incorrect, then you can get your money back for the ORIGINAL job. You may also be able to get the fee for towing, but you won't be able to get the money for the FORD job. The job of small claims court is not to make you out in a better position than before the 'wrong' happened. YOU decided to go for the less expensive job, and yes, you learned a lesson and should get THAT money back for trying the cheap way out. They are not liable for you now having to pay for the more expensive fix.
The documentation that you need is your DATED receipt from the transmission place, any written warranty that they gave you with the part, DATED report from the FORD dealer, and any other mechanic that specifically states the problem with the transmission and a DATED receipt for you new transmission from FORD.
GOOD LUCK!