Don't get your hopes up. Unless your motor is in like new condition, it is not really a collectable motor......yet. There are literally thousands of those motors out there....lots of them still running and being used.
there are thousands of tn 28's around and the td model also. the tn has a nuetral lever is what the difference is from a td. i bought a very nice looking and running tn 28 for $50.00. they are good running motors. they are not rare that is for sure.
I am thinking about fixing it. It runs but it really has no power. If I thought I could get a couple of hundred bucks for it I would sell it and get another motor. A guy I know gave it to me for my 14ft aluminum but my 55# thrust minnkota pushes it just as well and I don't have to mess with it to get it started.