I was culling through my stock of stamped rocker arms yesterday, looking for a set to clear the 1.5" O/D springs on my 360. Some are ground for clearance, I always assumed bcause 340/360 springs are larger diameter. Also, some have a more pronounced "detent" where the spring/retainer would be. I also have some of the supposed HD rockers, which seem to be stamped LH/RH vs. LT/RT, and I've found a weight difference of 15-20 grams. Again, this is all based on what I've found with the ones I have.