I can't speak for the springs, Gold, but I can tell you it'll be hard to stuff an L-60-15 inside the stock wheelwells without having them rub! I went thru this on my '68 and found it's all in the backspacing of the wheels to get the tires to fit. I got a set of 11.5x28 Hoosiers under my car, which are about the same height and a little wider than an L-60, but I had to order 8" Weld Pro Stars with 5-1/2" backspacing, and it's still a dang close thing. The things to look for are clearance on the outer wheelwell lip and spring and shock mount clearance on the inside. The extra arch you're talking about would certainly help, but with a tire that tall you might wind up with '69 that looks like a Funny Car! I'm using stock monoleaf springs in the rear with no problems, although I have Comp Engineering traction bars that keep the car from squatting and actually make the rearend rise under acceleration. The car has 15x5 Pro Stars in the front with the equivalent of E70-15 tires, and the car has a nice forward rake. But that's just my car, and they're all different. Hope this helps you in some way and good luck!