I can't help you w/ a 337 or field approval process for the skis, but can vouch for the Federal 2,500's being an excellent ski.
There isn't many PA-14's in the world, and there isn't many of the old original Federal 2,500's still around either...probably more skis than -14's though. That said, I can't imagine you having much/any problem making the skis "legal" for the -14.
You really do need to put UHMW (plastic) on the entire ski bottoms, not only does it GREATLY reduce damage & wear on the aluminum ski, it makes then slippery so thye can do thier job better. Throw the steel skeg away, down the center...don't need it, and don't want it.
Keep in mind that the federal skis have a parabolic rake and convex bottoms; "bannana" shaped front-to-back, and side-side. Take your time putting the UHMW on, you'll need to get creative clamping the plastic in place and make sure everything fits nicely before securing them permantly w/ counter sunk screws with nylocks on top. A lot of guys are running the bottom plastic out a couple of inches to gain some surface area....I make mine about 4-5" overall wider than the ski bottom. Easiest was to start the fitting process is to bend the edges of the plastic in a brake so you'll have a nice radius on the outside edges where the plastic sticks out...keeps from having other probelms if/when you slide sideways on glare ice in the wind.
Several ways to make a nice skeg system, on way is to use a sacrifical bolt head. As you lay out a pattern for the plastic, make one hole large to accept the skeg-bolt. Best place to put this skeg in directly inline with the axle, on the inside edge of the ski. Use washer to shim the bolt down far ebough to where it will make contact when you're on glare ice. Every so often as the "skeg" [bolt head] wears out replace it.
To prevent water from getting inside the tunnel (which frezzes, gets heavy & can break the tunnel), from the bottom when you're in the water (OVERFLOW), you need to make SURE the tunnel is sealed well before putting on the plastic. You can weld the original holes closed from the old metal skeg. Use some "5200" marine sealant around the base of the tunnels, boottom of tunnel to bottom skin, when everything is clean and preped well...then paint the skis w/ "silver" float paint.
