would this be the right ones for a 74 Schwinn Varsity?
 

http://www.amazon.com/gp/product/B00...A2TE9IQP68MWQU

would those be the right size? It is somehow currently the fastest bike I own (even faster than my 2011 KHS road bike, which weighs much less) It doesn't seem to be quite straight forward to figure just what size I need, beyond the whole 27", and the wheels are the only 'weak' point left that needs work.

Looks about right. The rim is the right diameter. Schwinns use a standard axle size, right? Not little ones like Raleigh uses. You might need to spread the rear dropouts a little but I don't think you'd need to cold set them.

The rear wheel will be fine.
The front hub on your bike should be measured. Measure the axle diameter and the inside width between the fork tips.

An undersize axle slot in the fork will need to be carefully enlarged with a file, such that the axle settles in with the rim centered within the fork crown.
If the inside width between fork tips is 96mm instead of 100mm, then I would bevel the tips with a file to make the wheel slip in more easily. You could also remove any un-needed washers from the axle assembly, if you have the tools and can adjust the hub bearings after. That would narrow the axle width by at least 2mm.

Some Varsity forks have slots with an oversized circular opening for a hat-shaped retention washer, but a normal axle assembly will also secure normally using the quick-release.

Looks like a nice set of wheels for a Varsity.