Wagoner front springs on rear cj7

I"m looking to extend my wheel base with the rear axle AMC20. I have been reading for hours now, I like the idea of the wagoneer front leaves installed in the rear of my jeep. My questions are, 

will the leaves bolt in with no modification needed to the spring mounts? 

Will my amc20 hit my gas tank so badly that I'll need to relief cut the fuel tank? My Fuel tank is the smaller one , 15 gal or 12 gal...  

I have a 2.5 lift SUA now and would like to leave the front leaves alone, and build the rear to match the height In the front. 

If I can gain 1.5-3 inches in wheel base by moving the rear axle back I would be very happy. 

To match the front 2.5 lift what wagoneer lift springs do I need? And where can I buy them new/used, no junk yards around me will have them im sure. 

Thanks for your help.  

I have never done this, but it is interesting to me and something I have thought of trying to do...although not necessarily on the rear of a CJ-7. I cant give you a direct answer, but I do have a set of stock Wagoneer/J-10 front springs here at my house. I am not sure if the tank will work or will get in the way having never done this on a CJ-7? I suppose you could take some measurements and make some guesstimates, or wait till you have the parts next to you and the Jeep. The Waggy springs are 2.5-inches wide so the spring should fit in the front spring mount brackets, but I don't know if the stock location for the spring mount brackets on the frame is in the correct place to locate the rear axle where you want it. You may need to move the front spring mount brackets to fine tune the axle location. Also you will need to figure out new rear shackle mounts. Maybe attached to the back of rear crossmember?

The springs I have here (off the front of the Piggy the Pig truck, '78 J-10)have the center pin about 22.5 inches from one spring eye and about 24.25 from the other spring eye. So if leave the front spring mount bracket and you measure back from the center of the front spring bolt to 24.25 that will roughly be the new center of the axle with these springs. 22.5 inches from this point will be the rear shackle.

Also You can get these springs new from BJ's Off-Road at www.bjsoffroad.com

Hope this helps. Let us know what you do and find.  
P.s. I am not Dr. Vern (but I am happy to take credit for his writing!)