| My advice is to take it to a reputable luthier in your area - it shouldn't take much time, and won't be that expensive, maybe a few bucks more than a set up (the bass will probably need a quick set up after installation). If you can, hang around and watch him/her do the swap - so you'll learn for next time.
If you do it yourself, remove the strings, remove the existing bridge, measure and note the heights of the old saddles with the tail piece using calipers. Use long straight edge (metre rule or similar) to mark the centre line (use a soft pencil or something removable if body is lacquered). Don't trust the position of the original bridge - you'd be surprised how far off these things can be mounted in the factory, also necks are not always set perfectly. For intonation you should only need to adjust the saddles in the direction away from the neck, and you'll only need around 1/4" adjustment (maybe a tad more if it was a 5'er). So measure from the string witness point of the saddles at their most forward adjustment - 34" from front of nut, 17" from centre of 12th fret, 8.5" from centre of 24th fret (if you have one). Make sure it really is a 34" (863.6mm) scale! - Yamaha's have an 860mm scale, some old ibanez's have an 850mm scale etc. etc. (measure from the front edge of the nut to the centre of the 12th fret and double to check scale length). Try a few old strings on the new bridge before you go ahead and drill. Make sure you have a good break angle across the saddle. If too shallow, install the tailpiece a little forward, but make sure you still have enough space for the fatter wrapped part of the string that's just ahead of the ball end - this varies amongst different strings, so leave a little lee-way here. Use a sharp drill bit and a centre punch for the holes, also make sure the drill is square to the body - you can use a drill press if you like, but its fine to just use an electric hand drill and something square to site it with. Poke the screws through the new br and mark the drill bit at the right length. If the bridge needs slots filed, do this now - put it in a vise with protected jaws, and use nut files or maybe jewelers files, but work out where the file is the same thickness as the particular string (use calipers). Next adjust the saddles to the heights that you noted, and install (saddle heights will still probably need tweaking, but this will be a good place to start). Oh and if the new holes are too close to the old ones, you have little choice but to fill the old ones. You can either drill them over size and fill with dowels, or use the old tooth pick and wood glue trick.
Hope this helps! | 
