How difficult is it to rebuild a C4 or C6 with a rebuild kit?

I have a bunch of old ones needing rebuilt and I've checked on rebuild kits and they seem to be worth the cash given that the return from selling a good rebuild is appealing.

Thanks,
Eric

 

I just got done rebuilding my C6 and I didnt have a book or anything bought the TCI maximizer kit from summit for 200. Never did one but I just took my time and every part I took off I replace it with a part out of the kit. Got it back to gather day before yester day and it seems to be doing good shifts hard into drive but that might be the shift kit. I say if you have basic mechanic knowelage go for it but take your time. A book might be a wise choice but I opted out cause it looked pretty basic to me.