i checked the casting number on my heads, i had them made for 72cc, 2.02/1.60, with screw in studs and guide plates with bronze guides. they were on my 357 until the supposed ".500" lift springs fell apart. is there a notorious problem with these heads? i noticed there was a helicoil in two spark plug holes and a rewelded area on the head where it looks like it was once cracked. anyway any info on these is appreciated.