Not sure what your plans are for needed speed but typically straight stock has plenty of power to push the A fast enough for most people. The only reason I'd see to add power is if you're climbing hills often with competing modern traffic. Then it could be important. If you have 60 HP already that's a lot considering original was about 40 I think! First issue with ANY model A is brakes. Stock brakes work great and will stop the car very well IF they are well maintained. Juice brakes are not necessary but maintenance of brakes of any kind to original specs IS. By your OP you probably are well versed in the Model A and probably already know all this but doesn't hurt to be reminded.
