The spring would be easy, but the rest would be difficult. I have built stabilized pans in N scale, and don't recommend it for the faint of heart. Basically, it requires at least one, and preferably two opposed, stabilizing bars, attached to cranks on the base "hinge rods". One crank for each bar is above the hinge, one below, and they are connected by the bar. That way, whenever one end raises or lowers, the other is forced to follow, keeping the contact shoe centered over the base.
The concept is easy. Getting everything aligned and the bar exactly the right length is the the hard part. It CAN be done, but I've only done it on scratchbuilt pans. Adding stabilizers to a pan that wasn't designed for the could be - interesting? frustrating?
I used the Ncat pans for years, until Overland Models released their Little Joes a few years back, then bought enough spare pans to outfit all of my motors. Expensive, but they work well, and look good. They're not designed for pickup, which I didn't need, and are closer to GN/MILW prototypes than to PRR.