Why not let go of SPSS instead? It has run its course and is basically legacy legacy software by now. But it good fun I suppose? Are you using SPSS as an oracle? (Guessing that the author is/will be in the comments.)

An oracle and fuzzing have been excellent when reimplementing software. Given implausible inputs, the black box shows its colours quickly. Rounding errors and different representations of floats are and endless source of debugging, eh, joy.