New to me 1982 305 CSR!

Put simply, I'm very stupid sometimes. It started raining after I got the front on and the temperature dropped. I had a blow dryer handy but it didn't do as much as I'd hoped.

Suppose I'll pick up some real tire lube this time too.

If you're using a lubricant, even dish soap, I doubt that's the problem.  But I don't know that much about changing tires as I've only done a few.  maybe head over to youtube for some videos. ???

This might be obvious, but once you get the tire started and it’s starting to get tough to lever over the rim, make sure the point of the tire 180degs opposite the tire iron is pushed into the center of the rim at its smallest diameter. 

The first set I put on my 750 were no problem, but it was like 95 and sunny. Thanks for the centering tip, I'll make note of that.