bought a set once for my falcon here >
http://www.whitewalltires.com/ coker is waaaaaaay too over-priced! unless you ask for slight blems. they still wtty them and they still look great. just a lot cheaper. as far as the size... go to the calculator at
www.1010tires.com and cross reference a few sizes in comparison to your old 20s. me personally, i would run about a 215/70r15 on it so that they have an old style feel to em ya know? that size would do fine on that truck! pm me if youve got any questions...