All depends on how much modification you are willing to do.

Seats in these trucks are pretty low already, so your best bet is a small sedan/hatchback of some kind. Vans, domestic trucks, Toyota Echos all have that high "command seating" that I think would put your head somewhere above the roofline.

Factory buckets should all but bolt in. Good luck finding a set for an 81 that are in anything remotely resembling reasonable shape. Not saying it can't be done, but you are going to have to do some hard looking to find them.

My Truck: 1987 XtraCab DLX 22R 4WD 5 Speed Manual
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"Speed has never killed anyone. Suddenly becoming stationary, that's what gets you." -Jeremy Clarkson