Rock Auto has the 20 gallon tanks for $81-$85 on 2 different brands. Look like the Fuel sender is $70. All these parts will add up quick. Have you considered good used tank with a Sender, lock ring and all already included.?
According to the application chart it appears to me any tank in an 87 up 91 squarebody truck will work. Both 2 and 4wd, 10, 20 and 30 series including crew cab dually.
CHEVROLET 10 PICKUP 87 gasoline, 20 gal, TBI
CHEVROLET 20 PICKUP 87 gasoline, 20 gal, TBI
CHEVROLET 20 PICKUP 88 gasoline, TBI
CHEVROLET 2500 PICKUP 89 VIN models "R/V", gasoline, TBI
CHEVROLET 30 PICKUP 87 gasoline, 20 gal, TBI
CHEVROLET 30 PICKUP 88 gasoline, TBI
CHEVROLET 3500 PICKUP 89-91 VIN models "R/V", gasoline, TBI
GMC 1500 PICKUP 87 gasoline, 20 gal, TBI
GMC 2500 PICKUP 87 gasoline, 20 gal, TBI
GMC 2500 PICKUP 88-89 VIN models "R/V", gasoline, TBI
GMC 3500 PICKUP 87 gasoline, 20 gal, TBI
GMC 3500 PICKUP 88-91 VIN models "R/V", gasoline, TBI