I ran a 7 on my sorely abused 80s road bike for the first year I did cross. Seven speed cassettes and freewheels are available cheap. You'll basically be running it as a single chainring. You might want to replace the 52 with a guard or a 46 or 48 ring. I put a set of cheap Sora brifters on a late 80s Shimano 105 set up and it still runs great.