You have a nice 90 there, but both of the 200E's look pretty much complete - so I'd say it's a decent trade. The plastic and rubber looks good on both of the 200's. The 200 engines are skookum. Like you say, they'll need a bit of tinkering, but it won't take much to get a decent runner going. I think you'll be happy with the upgrade. Besides, half the fun is working on these things!
On a side note, how can someone just abandon these trikes to the elements like that (sitting in the snow drifts). Man, it's almost criminal to neglect them in such a way.
1985 Honda ATC 250ES
1985 Honda ATC 250SX
1984 Honda ATC 200M
1983 Honda ATC 200
1984 Honda ATC 110