The commercially available blue foam block "kayak tie down kits" would be a good choice with your 1990 Olds. I think you can still find them for $29.95. IMHO the biggest reason not to use them is that, long term, they have the potential to do a job on the cars paint. Not an issue with the Olds I expect. Used properly, with a middle line through the cars windows and bow and stern lines they are suprisingly secure.

Mike Scarborough
Friendship Kayak