Eddy heads what rocker arm assembly should I use?

Chances are you simply have a preload issue as you think you do. It's not reserved for one type of block or head. It's more a combination of a bunch of things. The only way to get proper preload on any engine is after the longblock's together, you need to check it. Preload is the amount of distance the plunger in the lifter is pushed down away from the bottom of the plunger retaining clip. For most cams, and for the XE268 using the std type (822-16) lifters, you will want to have somewhere around .030-.040 of lifter preload. You should be able to go as far as .050 without problems. Anything under .025 or so might be loud. If you have the anti-pump-up lifter (867-16) then you will need adustable rockers because they are designed for much less preload and you'll need the adjuster to get it "just right". They will also be more noisey even when you get them perfect.