Dan, I agree about the FP7. It looked like others have already made a version, but I made it per a request from someone interested in a zephyr vista dome set I made. It insured that the train width matched the passenger cars I made.
I wasn't planning on making a standard J3 Hudson. Is there a significant amount of difference? Isn't a 20th century Limited a J3a?
I have started a Dreyfuss Mercury streamliner as well as a gg1. Have also wanted to do more steam locomotives, but they are difficult due to the width you need for the train motor. I typically print in batches to reduce the cost for making test trains, so it will probably be a few weeks before I'm ready to print again.
I made a Lionel Berkshire, however making a 2-8-4 locomotive presents a lot of challenges and therefore I decided the train was not a great fit for t gauge at the moment.
Another thing I'm planning to do is make a 3 axle bogie. I don't think i can make a motorized one, but I have a bunch of rail cars I made that need a 3 axle bogie. I made a wwII era artillery cannon that pivots as well as a whole set of steel industry rail cars.