The product you are referencing is a 1979 vintage unit. Since the surging only appears to occur at idle, this could validate your suspicion of a vacuum leak. I would suggest that you test for the leak, however my suggestion would be to use propane (vs. starting fluid).
Test first with the air cleaner hose off. Add a small amount of propane to the intake of the carb and if it smoothes out, this would indicate a leak may be present and is leaning out the mixture. Reinstall the hose and now test the common vacuum leak points with propane to see the response. This is much safer than using starting fluid, and the propane is heavier than air so it "sinks".
As far as obtaining drawings of the carb, do a google search on Solex 32 DIS carburetors. There is quite a bit of information available on the internet over and above our old Service Manual for the GM 72.
The Toro Company