For the valves I would ask the machine shop that does the heads for a recommendation on good quality replacement valves. Your build does not need stainless racing valves. Muscle Motors used to do a nice job on iron heads at reasonable cost. I don't know if they still do. If you need a shop for the heads, it might be worth giving them a call.

For the piston and deck height, it isn't really possible to make a 383 a quench engine without a custom piston or custom machining. Instead, the goal is to match up the parts to get compression in the low 9's to make a healthy pump gas engine. A zero deck piston would help get there. You need to measure the cc's of the head and deck height then use a calculator like the one linked below to figure compression and deck height with available pistons.

PS to calculate piston height: H=.5*stroke + rod length + piston compression height. Actually measuring assembled parts is an important check but you can use the formula along with measured deck height to check various combos on paper.

http://www.summitracing.com/expertadvice/popup.aspx?Control=CompressionCalculator