Well the average lift you get from a SOA is about 5.5 - 6 inches... but if you use 3" lift springs I would assume your lift is going to be 8" or more. The things you need to take care of with a lift like this are: extending the brake lines, installing a SYE and a CV driveshaft, and relocating the front track bar. Not to mention the "small stuff" like getting longer shocks, welding on perches and shock mounts, bleeding the brakes... Some may say you don't need a SYE but the rule of thumb is to install one with a lift over 4" i think... you may be doubling that so I think it would be a good idea.
One thing that concerns me is your 3" lift springs... are they CJ springs or YJ springs? The YJ springs are wider than the CJ springs and I would assume better for a SOA setup. I have never seen an SOA with CJ springs used but who knows it may be possible. I would just be worried about getting a negative arch after the spring over. The fact that they are lift springs may remedy that though.
Cost estimate:
SOA kit (RE) - 250
SYE and Tom Woods CV shaft - 525
new shocks - 125 or more
New tires to fill the cavern of space - ??
Regearing axles - 200 or more per axle
Able to go anywhere you Dang well please... priceless.
By the way I love my SOA...
hope this helps.
Joop