The alternator you have has a lucar connector, mostly used on older brit stuff lucas etc.
There will be 2 thick red and 1 thin wire, which will most likely be blue.
If wanting to use the alternator you have bought do as said, cut off the connector, now put a ring terminal on each thick red wire, this will need to be a 8mm yellow crimp connector, put this on each wire then apply a small amount of solder just onto the terminal wire, don't let the wire wick up the solder, it only needs a small amount, then connect onto the B or B+ terminal, you need BOTH the red wires, as one won't be enough on it's own under load.
Put a 6mm red or blue crimp onto the blue wire and connect this to the "IND" terminal.
Note you will have to cut the insulation off the terminal when crimped, make sure you do this well, you don't want much solder here as the vibration could cause the soldered wire to break.
All done.
tabetha