engine swap

I recently picked up a 1979 datsun 280z t-top 5 spd for $650. I think it was a good deal the body was straight no rust etc. I have heard of three engine swaps that interest me. A SR20, RB26DETT, and small block chevrolet V-8 does anyone know what would be the best power for dollar. my friends and I run a Z club here in oklahoma and I am the dominant racer while they build more show Z's I like the possibilities of the chevrolet power abilities for racing, but I'm not sure that being in a Z club if I should stick with the SR20 or RB26DETT. any ideas would be helpful.