To fit it, you first have to extract the  old 2-post bushes from the body (if
you instrument doesn't have bushes, fill the screw hole in the wood with a
suitable size wood dowl after drilling out slightly). Drill a 3/8" (10mm is
better) hole in a small bit of wood about 3/8" thick. Place it over the
bush to be extracted, and extract it through the hole in the piece of wood by
inserting a suitable screw into the bush and tightening onto a block or washer.
This will prevent chipping the paint of the guitar when extracting the bush. See
diagram below. 

Then, on a lathe turn 2 wooden dowel plugs (of similar wood to the body) to fill
 the holes of the 2-post bushes. Make them a push fit and apply a small amount of wood glue to the sides of the holes as well as the dowel before pressing them in with a drill press or similar. Make them of such a length that they don't quite bottom out in the hole so they will press flush to the surface of the body. The only concern here is that
 the wooden plugs will not be completely disguised until some sort of cosmetic work is done. This is actually the difficult bit. I would advocate leaving it until such time as a complete refinish is warranted for other reasons. 

 Next, the 6 new holes have to be drilled exactly 318mm (12½") from the
 middle of the 12 fret for correct intonation. I use a drilling jig made of Nylatron* (steel or Nylon will also do) which is clamped in position after careful alignment with the neck (using cotton or similar thread on E1 & E6 string lines of the neck to position the outside screw holes of the bridge) as well as being square to the center-line of the guitar. 

Care should also be exercised to ensure that the new bridge won't bind on the sides of the bridge cavity, if so, check if the neck can be realigned slightly
 to reposition the bridge away from the side of the routed cavity. Once
you have TRIPLE checked and are satisfied all is OK, you can drill the 6 holes perpendicular to the body with a 2.8mm or 7/64th" drill in a drill press (not with a hand drill). 

 Fit the bridge and carefully drive the 6 screws home making sure they stay
 perpendicular to the body as you do so. (An electric screwdriver is invaluable for this operation). This is important to avoid a situation where the bridge might bind on ill-fitted screws and therefore won't pitch centre. Leave the screw heads just off the bridge plate. It must pivot freely, without hindrance, on the 6 screws. That's why I made a proper jig (using a milling machine) to drill these holes. It locates neatly into the pickguard recess and is careful made so that it automatically positions the 6 holes in the correct position; alignment and intonation requirements satisfied. Make one if you are going to do a lot of these procedures. 

 The rest is just setting up the springs and saddles for height and intonation fine tuning. The Gotoh bridge, if fitted correctly, should require very little intonation adjustment since it is factory preset. You now have a proper Strat with a classic Strat sound. Have fun. 

                      HOW a drilling jig can help. 

 The drilling jig can be made from Nylatron which is an engineering grade black plastic (molybdenum disulphide filled Nylon used as a bearing material). It's really tough and won't wear out in the drill holes but is soft enough not to scratch the finish of the guitar; my jig has drilled hundreds of holes and is still tight on the drill bit. Nylatron can be purchased from RS Components (formerly Radio Spares) or an Engineering Plastics supply house. It comes in flat sheet about 3 and 6mm thick. Mild steel is OK if only a few sets of holes are contemplated, otherwise it can be case hardened (Put Masking Tape on the bottom of steel to prevent scratching). 

 Making the drilling jig. First, size and fit the piece of 6mm Nylatron to fit snugly into the pickguard recess. When in place, lightly clamp it at the end furthermost from the neck. Scratch a line 318mm from the 12th fret and at 90° to the centre-line of the neck ((parallel to the leading edge of the jig plate). Run 2 string lines from the nut (E1st and E6th) over the jig plate and tape them in place, 56mm or 2.2" apart, after positioning them parallel to the edge of the fretboard where the strings should sit naturally (the E6th should be a bit more in from the edge than the E1st). Dimple the positions where the string lines intersect with the scratched (318mm) line with a pointed scriber (not too deep).
 Preferably using a milling machine, line the jig up square to the traverse of the milling table and secure it. I use a pointed 6mm or ¼" ø brass rod mounted in the chuck for these procedures. Position this point accurately over the first dimple and traverse the table 56mm or 2.2" to ensure the 2nd dimple is accurately placed. Make any carefully thought out adjustments necessary to achieve this. Return the table to the start position and recheck the dimple position, then drill the 6 holes in the jig plate 11.2mm or .441" apart with a 7/64" or 2.8mm drill bit.