Question first:

Can I used a 6 3/4 action slide tube and forend on my 500, in place of the 7 3/4 tube and forend on there now?

Backstory

I'm relatively new to the site, but not gun ownership. Well, that might still be relative based on who replies. I've owned guns off and on for about 11 years now.

I was given a Mossberg 500 about 8 months ago, and boy oh boy was it in rough shape. When I got it, the entire action was completely jammed. I had very little experience with shotguns, so I looked around for a smith to take it to, and discovered I would MOST likely have to go at least an hour out of town to get any work done on it, so I pulled that beast apart and put her back together. Worked GREAT! Until I took it out, and it had trouble ejecting shells, and the safety works loose, so after a good round of clays, you go to pull the trigger and nothing. Better that I guess than the other way around.

So, I took it home, and stripped this thing to the bare bones. I even stripped the trigger group down, cleaned and reassembled it. Anyone who's looked at a Mossberg trigger group knows what I mean.

In the course of my work, I polished up the barrel where it seats in the receiver, and fine tuned the extractors, as well as cleaned up the mag tube, and the bolt, etc.

So, last weekend I finally got to take it out, and lo and behold, the wood furniture on the forend yanks the action tube nut off after ever 3-7 rounds, so the action and forend get misaligned, and I have to break it down, and reattach the nut. I finally got it pulled apart, made some mods(scraped away a slight amount of material from the front of the forend where the nut sits, so it can engage more threads) and put it all back together. I racked the crap out of it, and it seems like it will hold.

Since the gun was free, I'm fine going and spending 100-200 bucks sort of refurbishing it. I just didn't know if there's any issue using a shorter action tube on the gun, aside from aesthetics?

While you're waiting, the answer may be already in a post here:
http://www.mossbergowners.com/viewforum.php?f=17