First of all, I would like to commend you on your web site (had a quick boo). It's a little rough around the edges, but I like your approach to building a Samurai. Even if you are staying small by necessity (lack of funds), I still like it.
I too believe one can do a heck of a lot of 'wheeling and have a whole bunch of fun with a mildy built Samurai (235s ect.).
To answer your question:
I don't know anything about the National add-a-leafs, but I have heard that they are a good brand for "properly" built springs etc.
I just (as in yesterday, and tested today) installed a set of home grown add-a-leafs, and was surprised by the flex I achived.
I got a set of front CJ lift (2-2.5"?) springs given to me for free. I took the two packs apart and used 4 leafs, one for each Samurai pack, to give myself a little extra lift. They worked great today. I had plenty of flex, and in fact could have had more if I had time to find some longer shocks.
The problem most people have with add-a-leaves is the fact that they are "adding" a leaf to the pack, which stiffens the ride and cuts the wheel travel short. What I did was to remove some of the stock leaves when I added the add-a-leafs. In the rear I am running the stock main leaf and overload with the CJ leaf. In the front I'm running the stock main leaf and bottom (shorty) leaf with the CJ leaf.
This has worked well so far, I just don't know how long the lift will last. I suspect it well settle a bit after a wheel more. I would suggest having the main leaf re-arched to the same arch as the add-a-leaf. That should help with longevity.
Another idea that has been used (and Glenn W. doesn't like it [img]/wwwthreads_images/icons/smile.gif[/img]), is to bolt or weld some plates on the sides of the spring hangers to lower the spring mounting hole. How long are your shackles? If they are 1" longer than stock, you are now getting 1/2" of lift from them. If you lower the mounting hole by an inch, then you will get a full inch of lift (keeping in mind that there are drawbacks to this method).
If you can get a set of stock '76-'86 CJ front springs cheap or free, you could use your mainleafs with the Jeep leafs for a little lift too.
I've heard of people using Toyota Corrola, Bronco and Pony springs as well. Being a cheap SOB, I would go to the wreckers with a measuring tape, before I bought new leafs.[img]/wwwthreads_images/icons/smile.gif[/img]
My Zuk right now:
2" longer than stock shackles (1" lift)(no center brace off-road)
front brakeline brackets cut off frame
no spring clamps
31s rub a bit
235s don't rub
I need about a 2" longer shock for max flex, but it flexes as well as a lot of SOA Zuks I've seen