In all honesty, the only real fab work to do a guide is to drill two extra holes- one into your spring follower, and one into the cap of the springfeed. For the amount of time it takes to get the spring right by expanding the coils, IMO, adding the guide is more worthwhile. You can make the actual guide rod out of just about anything- metal rod you've got laying around, a wooden dowel, etc. Making the SA17 A More User-Friendly Primary
Lighter is better though, for the record. I used aluminum and am still trying to get around to ordering some delrin rod (just because I'm picky and want something "prettier" than wood since black delrin won't need to be repainted). Even the aluminum is heavy enough to slow the springfeed a bit, though not enough to cause an issue as of yet. It shot plenty of people out last weekend at EMR.