If you're looking for an engine swap, ease of installation, and lightest weight points you to an '88 HF.

If you want absolute lightest [but far more work], weight points you to an '84 1300 or an '85 HF.

Pretty much any D-series engine is swappable, and any B-series is swappable without a huge amount of work in an '88-91 CRX. H-series has also been done, but not common.