I have a question i have a set of used but in great shape proform roller rockers for a 302.There the one with the bolt allready in them.I cant use them because the 351 w i built needs the rockers that fits over the stud in the head.What are they worth they are in great shape with very low miles on them. Or should i just try to trade them for something else.I wouldnt know what to trade for. Can anyone help