My experience, is to buy a new radiator, well worth the money at a radiator shop and cheaper than online places. As for heater core, go new. Also since your there, might as well rebuild the blower motor with a chevy upgrade. Remember to use all new hoses and clamps and take your time, should be good as new.
85' CJ7 Laredo, 383 GM, Turbo 350, NP 203. SOA, 2" frame lift, 34" TSL swampers, Dana 30 open, AMC 20 w/ detroit locker, 4:10's, 1 Piece Mosers, 35" boggers to abuse when needed.