NAIRB outlined how to measure valve height. When you bought the springs there should have been some information with them that stated the installed height, seat pressure, coil bind height, and open pressure. If they are brand name, you can go to their web site and find out that info if you don't have it.
Most Chevy valves I've used install at 1.7" or 1.75". A cheap way to check the retainer height is to cut a piece of coat hanger to the desired height length. You can then use it to check each valve.
When you put the valve in, you place the spring in its pocket and place the retainer on top. Compress the spring and retainer, and place the oil seal (o-ring) in the second groove of the valve. Then put your keepers on and release the valve compressor. If you're using umbrella oil seals, you'd put them on over the valve stem before you put the spring on. I use both o-rings and umbrellas.