use ball valves and looooow pressures... dont want to launch the baby. i would probably use the cheapest stuff you can find. its not holding alot of weight so not like it should matter. just look around. i have seen some strollers that have shocks already. would make it easier to modify.
Here is a pic of my little boys Radio flyer wagon. It's lowered, bed linered, painted, chrome plated, sectioned tractor seat wrapped in ostrick pleather, and has a set of billet wheels. This pic was taken at Texas Heatwave in July.
i have one that i stretch ... it is 60 inches long and has a four bar neon kit. a battery box that holds a lawn mower battery it has red crush cushions and then there is one that i have dropped 6 inches. they are both for sale my youngest child is now 13years old. they are both in excellent shape