69 Dart - relocate rear leafs ?

All depends on how big you want to go for a rear tire.

With a '69 Dart if you install a DoctorDiff 1/2" spring offset kit you can probably get a set of 275's in there. Which is a decent amount of tire. And all that's required is moving the perches on the axle housing and bolting in the new hangers and shackles. Pretty easy and a great "bang for your buck" mod that doesn't involve a lot of fabrication.

A full 3" spring relocation and mini-tub will allow you to run tires in the 335 range, which is huge. But that requires the mini-tub. Without a mini-tub you're still stuck with 275's, because that's about all the stock wheel tubs are good for regardless of where you put the springs. The full 3" relocation and mini-tub is a fairly common modification, lots of folks have done it and I have definitely seen it done with the stock tank. Exhaust pipe routing gets to be a pretty big issue though, and I have also see a decent number of those cars with turn downs at the axle. Not saying you can't get a full exhaust in there, but it gets to be pretty strategic with routing.