Now we're talking my language.....woohoo a lifting project.
The leaf springs are easy....well the coils are too for that matter.
We'll start with the rear. For 6" of lift you'll probably need to do 2 different types of lift on the rear to divide the new stresses you're adding to the equation. There are 3 options: Lift block, lift shackles and add-a-leafs.
I'm not a big fan of lift blocks in larger trucks because they tend to cause axle wrap under acceleration. That shouldn't be much of a problem here though as we're not talking alot of horsepower. I'd use no larger than a 3" block due to the stresses your putting on the U-bolts. You can usually pick these up at an auto parts store for about $20 or you can make them yourself. Most are made of aluminum, which is not good on a larger truck but will work fine here, and can be shaved on the sides to fit your dimensions. You'll need 3" longer ubolts after you install the blocks. Most equipment dealers can make U-bolts to your specification.
If you go with 3" blocks, the shackle lift is also easy. I wouldn't do 6" of only shackle lift though. There is nothing complicated about a shackle so they are easily made. Find the length of the old shackle and make new ones, that are 3" longer, out of flat bar. Cut the flat bar to length, round the edges and drill the appropiate size hole in each end of each shackle. Add a spacer inbetween each set in the center for added strength. With both of those you have a total of 6" in the back.
Now to the front.
I would suspect you will need to go to a sping shop to have some longer springs made as there probably aren't many custom springs out there for your application. Bring your old ones so they can figure the specifications of your current springs.
It's kind of hard to tell from the pictures what the upper spring perch is mounted to, but you may be able to make a new mount to lower the perch 6" inches. This would give you 6" of lift in the front and you wouldn't need new springs (think saving $$$). This is the way I would go, if you have the tools to fab the needed parts, because springs are rather pricey.
Now to the fun part. Some things will no longer work and will need to be replaced. The shocks will need to be longer or you'll have to lower the upper mounts or raise the lower mounts. Judging by the appearence of the shocks, they might not be any good now. Removing them completely is an option since this probably isn't going to be your daily driver
.
Brake lines will need to be lenghtened or the mounts lowered if the brakes are hydraulic type.
Make sure your driveline will accommodate the lift in the rear. If the drive shaft is too short you will run into problems.
Again it's kind of hard to tell from the pictures but the steering might need adjustment. Best I can tell it doesn't look like it will, due to the geometry of the linkage. You might loose some steering radius to the left and right (how sharp you can turn) but the tires should still be aligned.
Again, most of this will be custom due to the age and application you are dealing with.
I found these people by searching "Cushman lift kits" in Yahoo. The kits they have listed are for the newer models but they may be able to direct you to a source for parts you need.
Parts4carts.com
Hope this helps give you some perspective and ideas for your project.
When it's done I want pictures. :drinkup