The altenator, starter & distributor will fit & work on an A14, although the advance curve of the A12 engine is different from the original one in the A14. The inlet manifold will not fit, but the exhaust one will bolt up to the head. Don't bother,... use either the correct A14 manifolds, or tubular extractors.

Also, use the engine mount brackets from your old cylinder block to ensure that the A14 will fit in without any fuss.