1998 Rodeo 3.2l timing belt change and rear brake drum

I currently have a 1998 Isuzu Rodeo 2 wheel drive, auto trans w/3.2l DOHC v-6 engine. I just replaced the timing belt and after idling for a minute or so the check engine light came on. It idles at the same rpm as smoothly as before with a faint pop in the idle, nothing different than before the change. After aligning the marks and replacing the belt, I installed the belt tensioner and it moved both cam sprockets about one-quarter of an inch counter-clockwise. I figured it was normal to do that and was such a minute move I finished the install, rotated the whole assembly to check for any binding which was none. Could this small movement be enough to cause any problems and if so how do you get around from keeping the cam sprockets from moving while installing the tensioner? I then moved on to replace my rear brake shoes, which i've done countless times before on other vehicles. I had no problems untill I went to install the drums (both sides) and they would not go on at all. All was installed correctly, new shoes were the same dimensions as old ones, adjuster was screwed in all the way and pistons on wheel cylinders were pushed in as far as they could go. The drums did not even have any ridges. Any help would greatly be appreciated.