There is nothing stopping you, using an A15 crank in an A14 block. As far as I know the A14 - A15 blocks are identical apart from the engine number stamping. 5mm difference in stroke, that all.
As for 180hp from an A-series on Webers, Im yet to see one. [I guess its not impossible] It would need some very serious money thrown at it. I would spend more time on building an A-Series that produces more torque. A correct sized / matched turbo will help you there.