Looks to be a '77 18/6, 1 yr only model( well, with that name). The other is a GT/18 which is a 78 or 79 model.
The 1 deck looks to be different, maybe it's a 48", the others are 42'?
The GT18 look to have a good grill, if ya parted, that's a $150-200 part on evilbay.
If the onan's are sounds, those are $250-400 running motors.
Snow blower may fetch $100-150 up my way.
3pt hitch would grab $125-150
I would say there is easily $800 in parts, but would be sad to part 2 complete tractors. I would consider offering 500, maybe 600 If I was in the market....
"But I'm getting out of the hobby this year"