dynamo to upgraded alternator

Im currently overhauling my electrics in my 2a, 2&1/4 petrol and have got taken out my dynamo to be replaced by an alternator.The thing is I wanted to put a higher output alternator than the standard 45a jobbies to run the extra lights etc.Iv been advised to go at least 65a.I havent a clue on what 1 would go in easiest or if i need to go for more amps.Any thoughts would be a huge help

Thanks.

The only bad things i can think of in changing (i did it my self some time back) are you need a different bracket, and i got a very good alternator from a good m8 of mine who is in the RAF for free its the one they use for the Wolf, and im told its one of the best, i cant help any more as im rubbish with sparks, and i mean really rubbish with them!!!