I have stewartb's PA-12 now, and have become a bit of an expert in the FliLite 3000's. For the paperwork, there is an STC, approved in like 1959 I think. It was issued before the requirements to have individual issueance of an STC per aircraft, so you may have to cite the STC if your mechanic can't use it alone with a 337. In any case it would be seemingly easy Field Approval with the STC. I have the STC and full and 1/2 size drawings and the approval 337 for my PA-12 with deviation for being on 3" extended PA-18 landing gear.
Kelly Verem sold all of his parts for FliLite 3000's to Burl, but Burl has not resold much of it other than to me, so he and I are talking about me taking possession of the parts. Tunnels are the hard parts to find, but I have one good one which I may make a mold of and have some new ones pressed and formed as an owner produced part. The slide strips are another wear item. My mechanic this year made a new set out of hard nylon with the right routered slots for my skis, and made up 3 extra replacement sets I have on shelf. He is tooled up to make more as well.
Stewart is correct about the rigging. I have all of Kelly's data, and the rigging for bungees and cables are different dimensions than original, but meet the specifications of 43.13 for ski rigging. I like the way they are rigged.
I really like the skis, and at 48lbs per ski they are a wheel ski that won't kill your empty weight like an AWB that is double that. I cycle mine all of the time on the ground, primarily when I am out at a remote location, I put a small piece of plywood under the tire location, and pump the skis up to keep them out of potential overflow or freezing down. Pump them down before leaving. I do it in the hangar as well when needed.
You can PM me if you want more information although I am headed to Ohau to flyfish for world-record-class bonefish and fly sailplanes Wednesday through Sunday.