Question about Heads and Rockers...

Pedestal mount and bolt down are the same thing. Stud mount usually require a 7/16" threaded hole for the studs - the pedestal mount holes are 3/8". So you've got some drilling/tapping to do on the heads if you want to go stud mount. That choice should be dictated by how you're gonna use the engine. The stud mount are more stable and will support more rpm - but since you're using the Y heads, you'll probably be fine with the pedestal mount.

1.6 or 1.7 is the ratio of valve lift to cam lift. The rocker acts like a lever arm so that for every 1 unit of cam lobe lift, it opens the valve 1.6 or 1.7 units. The stock arms on an HO are 1.6 ratio. So, swapping to 1.7's increases the peak valve lift by the ratio 1.7/1.6. Example - FRPP's E cam has a peak lobe lift of .311"; w/1.6 rockers, peak valve lift is .498"; w/1.7 rockers peak valve lift is .528". The ratio you go with depends on what the lift is on your CompCam, and how much lift the Y GT40 springs will take. I use the 1.7's on my Y heads with a custom cam (ground by Comp) and peak lift is around .535" on mine - I wouldn't go any higher with the stock springs. My combo is designed to peak low, so there's not much need to rev mine any higher than about 5400 rpm; depending on your set up, you'll have to make a call as to whether your valve springs can handle the increased peak lift of the 1.7 rockers. Hope that helps.