the 4inch lift would be easier to do that the spring over unless you are a good fabricator. my '70 has a 2.5" with 1.25 shackles and .5" poly bushings. , it easily clears the 33's i have on it. with a work i could probably fit 35's. i do know that a friend of mine has a 67 and he had a 4 inch lift and could fit 35's. its possible with the lift and in the long run easier than doing the spring over-i agree with jeeper03 on the axles if your going to do a spring over you might as well wait until you upgrade axles. i chose 33's because i didnt want to risk breakage on the stock 27 front.
1951 CJ-3A-Chevy V-8, 2.5" Lift Still Going Strong, but In need of restoration (eventually)
1970 CJ-5- Fully restored-saginaw ps, lift, 33's, rear locker etc.
1999 Cherokee Sport BB lift, 31's
2000 Cherokee Sport
2001 Cherokee 60th Anniversary