need some info on rear disc

im wanting to go with disc brakes on rear of my 73 challenger, where is a good place to check about these, and will they work with my rims that are size 15x8

Use front rotors from a 94-96 Intrepid or similar (Concorde etc) you will have to either turn down the axle flange just a bit or open up the rotor hat section with a lathe about 0.30 or so. Depending on the lugs you have you may need to countersink the lug holes in the rotors from the inside with a 5/8 bit. Use the GM metric calipers with E-brake like fat rodder sells on e-bay for $125 a pair loaded (with pads and bolts) and use the weld on metric caliper brackets from Speedway motors which are $9.95 each. The rotors are about $28 new from a discount store or cheaper at the salvage yard. You will need a couple of metric brake line or banjo adapters to finish out the line setup but this is by far the cheapest way to go. Make sure you position the rotors where the e-brake cables reach and the bleeders are on top!