good enuf. my concern is spreading the rear of the bike to accommodate a 700c wheel, IMHO this may weaken the steel to some degree. other then that, it's a nice feature.
I think you're making a much much bigger deal out of it than it is.
First, the wheel size is independent of the distance between dropouts.
Second- the 80s Treks are spaced at 128 so they can go to 126 or 130 with no mechanical spreading other than your fingers and minimal (I mean minimal) effort.
Third- think of all the 120 to 126 and 126 to 130 conversions you've seen here (and the millions more throughout the world in the past 30+ years)- and think of how many mentions you've read of a chainstay failing from spreading a rear end from 128 to 130.
You're tying your shoes together by not considering a different wheel set. If you're OK with the Helicomatic- take care of it- there's (a few) people that still have them running. I guess it's just suggested to maintain them a little more often.
Again- there's no real problem in staying with 27" wheels- the bike was designed for them- and there's still quality tires around. I've used both the Pasela 1 1/4" and Sand Canyon 1 3/8" tires. I just took the 720 to a 10 speed 130 rear end and 700c wheels. And I'm SO glad I did.
If you're curious about it- try it- you can always go back Just don't spread the thing to 135.
Good Luck!!!