Starting out with a 1300 dollar truck, we are about 2,000 dollars into it with 8.75 rear end and 3.23 gears leaving 3000 dollars for the drive train w/better gears. AND, we didn't sell one thing from the truck to lower the cost, like the power steering pump and box, the 318 roller cam motor, etc etc. which that money could be spent towards the build. Also, keep in mind, we found cheaper starts but we liked the truck. Examples, we found a long bed D150 for 500 or best offer with a bad 318 and a diplomat for 600. Pretty sure if we'd had started with the 500 dollar truck (maybe 400 would have bought it) we'd have had 3500-3900 for drive train.
