I feel ya on the funds, took me a long time to save and I shotcutted a few things, and still went over budget
I have to defer to cam's comment on the max width, I'd try to match width and go with something about the same length as those offered in the kits. The important part is That they aren't too wide for the spring pads and shackles you are using. I suppose at some point you'd interfere with brakes and shock mounts but youd have to go really mode for that I think. At one time I knew all the numbers but I've forgotten so you'll have to do the research, if necessary i suppose I can go measure some of the kit stuff for ya as a reference but I won't be back home for another few days.
from what I remember though if you move your rears to the front and go with chevy 56" or 63" (guessing but I'm pretty sure it's one of the two) it shouldn't be too hard to stay fairly level and get good geometry by playing with shackle length and mount/hanger location. Bet looking through some builds on here would help you figure out what has worked for others, I took the easy way out so you'll know more than me when you do figure it out. Good luck.
