If you are missing hardware, that happens to all of us. Just determine the type of hardware (screw or bolt), thread size and length. For bolts, normally grade 5 hardware is plenty strong enough. The bolt heads have three hash marks radially on them at 120 deg apart.
The length is determined by the "stack". The stack, like the "grip" in rivets, is merely the thickness of all parts being joined, including all washers and some extra stick out length. A good rule of thumb for extra length is about 1 diameter of the fastener. Then round up to next available length. The bolt should "stick out" past the threads or nut. Hardware store bolt length increments are sometimes large. (1/4" or 1/2") If you are trying to match an original bolt, you may not find that exact length due to the fact that the factory had better access to smaller length increments or a "special". So just round up.
Use lock washers and flat washers, not lock nuts. The lock washer goes under the head if no nut is used or under the nut, if used. I know you know most of this, just covering all bases for posterity. Most of the time real tight is good enough without a torque wrench. As long as you realize the size you are tightening and do not use extra length wrenches or use two arms. On small threads, keep your hand near the socket end of the ratchet wrench. Not out on the handle.
I use my "weak" arm and tighten until my elbow clicks.
You must be careful with bolts under 3/8. Don't go crazy on hardware that won't hurt if they come loose, like the heater control. Motor bolts, steering bolts, drivetrain bolts and wheel lugs need to be tightened to spec with a torque wrench.
You should go around the truck before assembly and "chase" all threads. Use a tap gently into the female threads. Use a die gently on all bolts after they are wire wheeled clean. Hardware will then go on nicely. Many times I have run into hardware store fasteners that don't thread in nicely. This is due to zinc plating on them being out of spec (Chinese). Either find better hardware or just chase them. Zinc plating can be pretty sloppy sometimes. Cad plated was stopped for awhile due to health reason. Galvanized is not used for automotive. Black phosphate/black oxide are good.
You don't need ARP high strength and you don't need stainless bolts for general use. There are some good general automotive fastener suppliers and FLAPS.
There are some specific types of bolts for the body, like fender bolts with a built-in "washer", called flange head. There are bolts with a "lead-in" point. Suit yourself as to if the specialness is necessary. Most times there is a good reason for them.
