I am wanting to lift the rear of my buggy up higher for the farm. It has swing axle rear at the moment and just dont want to have too much positive camber.
Will the IRS gearbox bolt onto the floor pan?
I will weld up supports etc for the axle so i can have more lift.

Yea that would work you can buy parrts for a conversion you want to get the geometry right. but the rs and swing boxes share the same boltups

Will the IRS axle bolt onto a swing axle box?

Nope - to go from SwingAxle to IRS (double jointed axles) you need to change the gearbox, axles/drive shafts and spring plates.

You also need to add the pivot arm boxes (the bit that requires welding) and also the diagonal arms.

It's not a simple or quick job, but definitely do-able. Best starting point is to find yourself a donor IRS rear-end...