Just an fyi Rock Auto keeps us updated with new discount codes in the Vendors Warehouse section here on TTS. Click on Rock Auto.
http://www.thetruckstop.us/forum/forums/rockauto.405/
Tough call, those plastic rocker arm locater buttons can fail and get noisy but that's usually associated with a broken pushrod and a miss/backfire
Any smoke or dropped cylinders?
Valve job? Check for pitting/erosion on the port side of the exhaust valves. Check for cracks between the In/Ex valves. Guides hold up pretty well but worth a check also. Strait edge the decks check for warpage. Usually they're pretty sound if they lived life on a n/a motor.
There was a YT video posted by @SmithvilleD a long time ago (iirc) of a Powermaster on his rig. It cranked fast. Sounded strong. Would be curious of what kind of service he got out of it.
On my 6.2 big valve heads the tang that locates the pre cups in the head pockets were on the opposite sides compared to my 93 6.5 heads with the T pre cups.
I kinda milled the 6.2 n/a cups to my *spec*. And felt great doing so. :)
Other differences could be injector angle and injector body thread pitch. It could affect fitment depending on what lines, manifolds etc you want to run.
The inline device is a piezoelectric trigger that works with a strobe.. I thought there was a special timing light deal for these at one time. TT1000 maybe? I can't remember.