Weak points? It depends. How hardcore are you planning on getting? You can run up to 36" on a open front diff without problems. As soon as you lock the diff, you'll start breaking the CV axle, otherwise known as the "birfield". The best fix for that is www.longfieldsuperaxles.com
There are other weaknesses, but those only show if you run 40" tires, locked, big HP or super low gearing, chromo axles, etc etc. Axle housings have been known to bend if you jump them too hard or run into a wall doing 60 <img src="/forums/images/graemlins/zombie.gif" alt="" /> You can buy or make axle and knuckle gussets such as the ones from http://www.marlincrawler.com/htm/armor.htm
Axle widths? What rig are we talking here? Here's some Toyota widths
Toyota Axle Widths:
(all widths are measured wms-wms, wms=wheel mounting surface)
* '79-85 front axle~ 55.5", rear axle~ 55"
* '86-95 front IFS~ 59", rear axle~ 58.5"
* Tacoma & '96-up 4runner front IFS~ ???, rear axle- 60"
* T100 front IFS~ 65", rear axle~ 66.75"
* Tundra front/rear~ ??
* '90-97 Landcruiser FJ-80/FZJ-80 front axle~ 63.5"
So, the front axle is 55.5". If your wanting to go 61.5", I think your best bet, if your determined to run Toyota axles, is to get a custom housing made from www.diamondaxle.com
or run a FJ80 front end. Spacers work just fine for 3" or less as long as you properly torque them down and check them every once and a while. But I wouldn't recommend 7" spacers.
Toyota e-lockers are the way to go. Strong as anything Toyota. Dependable. They can be manually locked and unlocked in case of the locking mechanism fails (either the electric locking motor or a downey cable setup) You can get a used e-locker for $300-$500 and drop it in with a few modifications http://home.4x4wire.com/adamf/88/elocker.htm
Then there's the ARB. Nothing wrong with it really, it works. But if the air supply is cut off (broken line, compressor takes a dump, etc) then your locker unlocks and you cannot manually lock it back up. Plus you need a source of onboard air ($200 on up) and you wont find a used ARB ($700 new)
Any other questions let me know