You should be able to reuse all your parts. Keep each retainer with its respective valve and lock combo. Inspect each part closely for cracks and what not. After you put the springs on lightly tap the top of each valve with a soft rubber hammer to make sure all the retainers are locked tight.
Be very careful to measure the height of your exhaust springs. Some Chevy cyl heads use a short exhaust spring with the rotator. If you find your heads have short exhaust springs. You will have to replace the rotators with intake valve type retainers to use the aftermkt spring.
If you try to use the aftermkt spring in place of a short spring, and then try to use a rotator , you will have plenty of problems.. I have inexperienced people do this and then can't figure out why they bend pushrods. As you are now into the .480+ lift with the extra ratio rockers.
As long as the rockerarm geometry is correct, you should get more lift. If the pushrod length is off, you could loose lift. I've played with that several times and found that it's easy to get a surprise. As far as more duration, the cam is not moving the lifter any longer, the mechanical advantage has been increased for more lift. Set up a dial indicator on the retained parallel to the valve stem and check before and after.
Well we are going deep. like i said it is just a slight amount and Bob said"You couldn't feel it, see it, hear it, barely measure it, so I say NO! it keeps the kids out of trouble...". I'll go with that but to NONE...It is not entirely true.
The valve attains .050" faster and it closes to .050" later so there is, slightly, more duration at the valve and that is really what matters, not the lobe.
Overlap and seperation are angles, they will not change one iota.
These springs are made by several places (at least three) and sold under about a hundred names.. You have to look at the seated pressure (usually around 85lbs) and the lift that they are rated at.. Some are .480 and some are .500-.510. Prices vary, even for the same springs. I used to pay $.37 each for the .480 rated ones.