Don't forget that if you insure your '81 at $21,000. Take tons of pictures, get an appraisal and document, document, document. If you don't, the insurance company will determine on their lonesome the value of your car. If you try to overvalue your car, it's not the insurance company's fault. You'll also pay more than you should anyway!
If you get the car painted or whatever later on making a big difference in value, make sure you adjust accordingly..etc.etc
Also, check the differences on deductible costs. It's not that much more to go $500.00 or even $250 deductible instead of reaching for the $1,000. Remember your insurance company will not defend you if you do not reach your deductible. I had a claim a few years back for $950. and tried the $1,000 deductible route (not anymore). They would not defend me and it went from a sure 100% other driver's fault to 50/50 both our faults even though the accident report was in my favor.
Chuck M