Suspension- want to level it out, what's the best way?

[azlamm65GMC]

I am restoring a '65 GMC half ton short bed/step side, it's a surprise for my business partners father in law as it was his truck he bought brand new back in the day and we found it and are restoring it back to original. We are going to throw a couple of our own touches to it and one is just leveling our the suspension, has that squat in the front and would like to just lower down the rear to make it level. If it was my truck I would put a 3-5 lowering kit or put it on bags. The truck has the leaf springs in the back and have looked at those shackles that lower it. Just curious if anyone's ideas for leveling it out bc I have it down to the frame right now and it will be easier to do the suspension work now while the body is off. Any suggestions please