Advice on changing from stock 14 inch rims and spacing

You can check your backspacing by removing a rear wheel and putting a straight edge across the drum where the wheel mounts, then measure the distance from the edge that touches the drum to the leaf spring! You will want to subtract an inch or so from the measurement to make sure that you have some clearance between the tire and the leaf spring, so for instance if the distance between the drum face and the leaf spring is 5", you would like your backspacing to be about 3 1/2"! Then you can do the same thing to figure the width of the rim...using the same straight edge against the drum, you can now measure the distance between the drum face and the inside of the wheel lip, and subtract about the same clearance number! So, for instance, if the number between the drum face and the wheel lip edge is 5", you would subtract about 1 1/2", making that number 3 1/2"! Now add the backspace and the front number together, or in our example 3 1/2"+3 1/2", and you would be able to run a 7" rim with 3 1/2" of backspacing!!