Actually it won't help you. I noticed that for some reason, all rebels have more blow back than the average blow back gun.
I don't know why, probably a problem with the length of the bolt.
anyhow, PM spud majic and order a bolt from him, and a valve if you want.
They are teflon, have no o rings, never need oiling, last a long time, and and super duper high flowing. and they stop the blow back problem
I ordered my valve and bolt from him and should be getting them soon, i'll inform you when i get them.
So you don't need vertical feed, it won't do you any good, especially since AGD did a test and vertical feed can feed balls up to 15 bps without bumps or skips and powerfeed can feed 18 bps without bumps or skips.
This depends on the gun being used but in this case, with blow backs, its true.
and to answer your question, you can't make it vertical feed YET. I think you may be able to buy a rebel LE body for it, but they take different grip frames