How to figure the basis for this redemption?

Your basis is the amounts you've contributed to the policy and the reinvested dividends. See the IRS tool to determine whether the insurance proceeds are taxable.

It is probably not going to be easy to figure out how much that is. Hopefully the insurance company would maintain records that help establishing that, so I'd suggest starting with asking them. Otherwise you'll need to find old bank statements and insurance statements to figure out how much you've contributed throughout the years to that redemption accumulation.

If I understand correctly how such insurance policies work, it is very likely that you paid into the policy more than what you're getting out of it. But you do need to have proper documentation to show that in case the IRS has questions. For a 19K redemption value of a 60-year old policy, you need to show that you've paid, on average, at least $26.39 monthly into the policy (adjust the math to the actual values in your case).