I have read where others have used the less expensive 1.94 and 1.60 chevy valves in their 351Ws. I have a set on Comp roller tip rockers that instruct me not to use the shorter tipped valves. Are my only options to buy new 351 valves or change the rockers??? If I use the chevy valves do I also have to buy chevy retainers and keepers??? Does the 1.94/1.60 combo make that much difference in HP that a person would modify newly rebuilt heads (stock valves) that are complete and ready to mount??? Does the fact that the heads are aggressively ported have any bearing on the valve size I should use? I do not want to spend several hundreds of $$ for a valve job, new valves or rockers etc. on perfectly good heads if I am only going to gain a few extra HP. Thanks for any help.