The suitability of an engine is more down to it's condition that whether it is A or A+. Either has the potential to produce more power if is in good nick and you bolt on the right goodies.Just a question now of whether to keep looking for an A+ or to settle for a standard 1275 A unit
The great god Vizard has calculated that a good manifold is worth 6 to 8 bhp alone. This and the larger carb is where the A+ gets the extra power from.