Can't really recommend on companies as I've always rebuilt them myself.
Fitting is fairly straight forward if you're mechanically competent and can be done single-handedly, although it's
much easier with two people, especially if you've never done one before.
You'll need to remove the backbox and drop the mid-pipe down, and on 3dr models you'll need to remove the strap that goes from the beamtube underneath the fuel tank (just drop the strap as the clamp will have very rusty fittings). Free off the brake lines and remove the drums (large hubnut to remove the drum/bearing, and then 4 x M8 bolts to remove the drum backplate with shoes etc still attached). It's easier if you disconnect the handbrake cables from the lever, but you can leave them attached and untangle them from the beam later.
Beam should then be in a position where it can be lowered down. Put a trolley jack underneath the centre of the tube, and then in the boot there's one nut either side under a round plastic over for the rear sandwich mounts (undo these first) and then two nuts either side at the front just behind the rear seats. Undo those and carefully lower the beam down, supporting it as you do as it'll try to twist and fall once the studs are clear of the body.
Refitting is the reverse of removal. Getting the beam aligned is where a second person helps massively as you need to keep it aligned and jack the trolley jack up at the same time, which is awkward by yourself.
Before refitting check the condition of the rear sandwich mounts as they're usually shot (they split in half) and wise to inspect the brake lines, wheel cylinders etc as they'll no doubt be looking distinctly second rate if they're original. Oh, and when refitting the shocks, make sure the bolts go through from the inside outwards on the end that's attached to the mounting arms (ie upper ones when it's on the car) - if you do it the other way, you won't be able to replace the shocks on the car without dropping the beam.
