If you're asking about which swing arm to use I'm assuming you want to do a modern type rising rate suspension with upright shock.
If wanting to do old style cantelever monoshock you could use an original swing arm with the loop welded on and the shock top mount welded onto the frame under the seat and the shock nearer to horizontal, I did this style on my avatar bike, its much easier to do than a rising rate modern type conversion, I used a Fazer 1000 shock.