can they be installed without the valves touching the pistons?
Yes. I have roller rockers on mine, and I'm running .515" lift with flat top pistons. Still, it's a good idea to check before you fire the engine. Put some silly putty on the piston, set the head on the block, and spin it through a cycle and see how thin the putty gets spread.
does it take replacing the pushrods etc.?
Typically, no. On engines with fixed rockers, it's common to have to change pushrod length or change lash caps. Our rockers are adjustable. You do need to check for pushrod clearance in the head. A 1.6:1 ratio moves the pushrod closer to the upper edge of the holes the pushrods pass through in the heads.
does the pcm need to be modified?
It shouldn't. The difference between non-roller and roller rockers is only a horsepower or two. If you rev to 7000 you might see five horsepower. If you also move up to 1.6:1 ratio rockers you're gaining about 5 horsepower across the rpm band, which should be within the capability of the stock tune. 1.6 rockers do nothing to increase your duration or change your lobe separation angle. It's simply a 7% increase in lift.
what is a "full" rockers as was mentioned couple of times?
There are roller-tip rockers, and there are full-roller rockers. The roller-tips have been dyno proven to be nearly worthless compared to the expense. Full roller rockers have roller bearings in the tips and in the fulcrum. It's a situation where you shouldn't deal in half-measures. You either need full rollers or you don't.
If you want some quality 1.6:1 stamped rockers, these Elgins have been suggested.
KMJ Performance
www.kmjperformance.com
Proforms are cheap. I used them on my engine, but I'm also running beehive valvesprings, which don't have a ton of spring pressure. Knowing what I know now, I would have gone with the Elgin rockers above. I wouldn't trust them for 7000 rpm operation, which is what justifies roller rockers over stamped rockers. Skip 'em.
Scorpion and Crane are supposedly pretty good, and not horribly expensive.
Harland Sharp is the gold standard of roller rockers, and they charge gold prices.
and what's the benefit providing i got the vortec fuel pump?
First, you have to understand that the factory stamped steel rockers aren't actually 1.5:1. It's more like 1.48:1, and at high rpm they flex to about 1.45:1. If you have a mild motor, they're good and dirt cheap. Failures are really rare, which can't be said for aluminum rockers.
If you're not building a 7000 rpm motor, get some longer-slot stamped 1.6:1 rockers and ensure your pushrods have clearance.
If you're building a 7000 rpm motor, buy quality full roller rockers.