OEM Samurai axles are mounted underneath. However since yours have been moved to the top I wouldn't change that. It is probably one of the most popular suspension modifications done. Driveline degree angles for the front drive shaft are 8 degree and 10 degree for the rear drive shaft.

welcome to Zukiworld.... 

The stock springs come mounted under the axles. The previous owner of your rig has moved them on top of the axles. If you get stock springs and mount them under the axles (like it came from the factory) your 31 inch tires won't fit anymore. You can mount stock springs on top of the axles (without that block), or mount aftermarket springs with a couple inches of lift under the axles, and you should be able to keep the 31' tires. You also might want to look at the shackles on the end of the springs to determine if they are factory length or not and if they are safe. Given the suspension you have, I would guess they are likely not original. Post pics if you are not sure and I'm sure we can tell you. Are you in Arizona? If so, where? I am coming down there next month and would be happy to take a look at it or give a hand if you are near where I am headed.

I've added a pic of the front and rear shackles, used a tape measure to give a little more of an idea how long they actually are.

sorry about the late replay by almost a month, I recently started a new job and it's been crazy in my house with the flu and the kids and all the other stuff that we all deal with day to day.

Tose are OEM shackles. I would avoid longer one's but the stock stamped steel shackles are pretty weak. I found a set that was only 3/4" longer and seemed to work pretty well.