What sort of budget have you got? The most obvious option would be an engine swap, 7M-GE or GTE, 1JZ-GTE, 2JZ-GE or GTE, 1G-GE GTE or GZE would probably fit (not being an expert on 78 Cressidas i'm not entirely sure)
Failing that, you could do some mods to your current engine, but I doubt it'd be worth it in the long run.