[lynxrpken]

well there are two ways I see to do this

lets start off with the easy way that I think is dumb and i'll tell you why I think it is stupid. use storm troopers as your basic gaurdsmen you will need to modify the hellguns by drummeling off the cord on the butt of the riffle. I would also get rid of the antenna on there backpacks.
I do not like this idea because you are not going to be able to use stormtroopers. this is because if you use something to be something else every occurance of it in the army have to match. this means if you use stormtroopers as gaurdsmen every gaurdsmen in the atmy has to be a stormtrooper also every stormtrooper has to be a gaurdsmen.
now the way I like is to get a lot of lasguns like 150 of them. this is easier than you think. I have a over 100 piece IG army and all of my troops are mutant rats. I have sone it, it is not hard to get the guns. what you will have to do to make it work is
1) drummel off the hellgun compleatly. it is easy. also need to get the cord off.
2)the box on the chest will need to be made for every modle. it looks like the bottom half of a cadian vox pack will work for this. you will ned to use greenstuff for the binding that holds it on.
3) obviously the lasguns will need to be modified by cutting of the trigger assembly and handle then affixing them to the modles where the hellguns where.

it is going to look NICE if you use the second method. it is going to be hard though hope you are ready got a challenge. someone on here is making a entire army modification using only ratling sniper modles. I made a rat army. so it can be done. let me know if you need help