OK, 1st off, thanks in advance for your time. The problem: 97 3.0 vulcan with cracked heads. The casting numbers are F6DE. I have available a set of A920 heads which look identical (I think they are for the flex fuel) and a set of F6DE's with the smaller 7mm valves. Will the heads with the smaller valves work with the same rocker arms as the heads prior to 7-13-98? If not, can I use the FFV heads?