Hi Chris,
The only ERIE book I have for reference is "The Erie Railroad Story" by Paul Carleton.
He has several pictures of the original FT's but I can't see any numbers on the "B" units. Later on, as you mentioned, ERIE renumbered them to the 70XX series. These have numbers on the "B" units.
I bought two sets of the Lifelike Alco FA1/FB1 with number 729 and they make a great looking lash-up. I also have two sets of the earlier Lifelike F2A/F2B with number 737. The older F2 sets only had the "A" unit powered so I bought extra A units and modified them to fit the "B" unit shells. The F2 lacks flywheels and the split-frame chassis but I still like the little "growl" they make and the power is there.
Lifelike has redone their FA2/F2B with split frame and flywheels but has not done them yet in ERIE.
The new Intermountain FTA/B's are beautiful and now I see Intermountain is coming out with a line of F-3's. ERIE is not in their original release but I can hope for them in a future release.
For so long there were almost no ERIE locos in N-Scale. Atlas made their beautiful RS3 and GP7 and then Lifelike gave us the FA2, FA1, PA1 and E8...things are much better now for ERIE guys like us.
We could use a switcher in ERIE livery.