timcupery pretty much summed things up, but just to chime in...
I did this very thing with an 8-speed cassette several years ago. My road bike had just gone out of commission from a cracked dropout, and there were several races coming up that I wanted to participate in. Using the road crank that was set up on my fixed gear conversion, I spread the 126mm triangle apart to accept my 130mm wheel, hooked up a downtube shift lever and derailleur, and was in business. While I never actually raced on that setup, it was certainly a fun experiment.
Perhaps the only thing that I might recommend would be to take a good look at your chainline once you've got the 7-speed wheel in there. Obviously, since you've only got one chainring, the chain angle is going to be pretty extreme when you ride in the very highest and very lowest gears, thereby increasing your chances for a thrown chain. Assuming that you've got a 42mm chainline with your Sugino 75's, and Shimano's spec for chainline is 43.5mm to the middle of a road crank (41mm chainline inside ring, 46mm chainline outside ring), your chainline will be 1mm off spec in your easiest gear, and 4mm off spec in your hardest gear.
Given this, it might be advisable to invest in a chainkeeper (like the Deda Dog Fang) for a little insurance in your easiest gear. A chainguard would give the same insurance in your hardest gear, but I'm not sure if you can install them on a track crank. If it's not possible, perhaps the best insurance would be to simply avoid all-out sprints in your hardest gear.