Hi Duane - Welcome to the site.
I've got a 66 Jetstar 88 I'm working on. Not much crosses with the Cutlass that I know of. Maybe small rubber bumpers & grommets, don't know.
Fusick is the number 1 Olds restoration supplier. But I don't think they have seat covers or door panels for 88's.
www.fusick.com They do have carpet & headlines.
SMS Auto Fabrics (
www.smsautofabrics.com) should have the correct seat material. Then have a local upholstery shop recover the seats. The local shop maybe able to match your material a lot cheaper than SMS. SMS can custom match/make your door panels.
For bumpers & sheetmetal try this site, ebay or
www.realoldspower.com. I've been looking for a right front fender for my 66 for about a year. I have seen 65 sheetmetal, but 88 (&98) parts are hard to find.
For the taillights and grill I'd watch ebay.
Don