The front suspension is fine for the stock ride height. When the height is changed then the ride suffers because the control arms are no longer anywhere near level. If you could alter the front to get the control arms more level, then the handling and ride would improve.
For the back, IRS is great but how many people have done that, plus how much work was it? The big limiting issue in the back is lateral control, leaf springs don't do well naturally for that. If, big if, if you can find a way to mount a panhard bar to the rear frame, that would solve the back end issues for most applications. Before you jump deep into the IRS project, why not climb under there and see if you can fit a frame bracket inboard of the leaf on one side, to run a PHB to the other side where a diff mount is easy.
The front coil over swap needs reinforcements for the upper shock mounts. I hope to go that route some day, for the better ride. The back I'd love to do something with, but the IRS is too far I think. Regards,