It is quite simple to do a basic longshot mod for free. not 120 feet mod but getting a good 60 feet. http://www.youtube.com/watch?v=9uQBg4mKXmI
is the link to Drac's longshot mod. it gives simple instructions on how to open it up and to take out the AR's. after you take out the AR you can do a spring replacement. i know you dont want to spend any extra money so you can always gut one of your other guns to get said spring. the recon spring works PERFECTLY for this but since you have put work into modding the recon you may be bit hesitent to do this. it is ofcourse just a suggestion but it is an option. on the bolt sled find the small hole that steals air and seal it with tape. if you d odecide to do this I would also recomend that you take the raider drums to use as the clips for teh longshot. and since of its light weight the alpha trooper can be used as a secondary using the smaller drums.