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Bamboo812 wrote:The LWB swingarms had more bracing from the factory than the SWB does. I've seen guys extend the swingarm even further for more suspension travel, and they added more bracing, but this was for off road applications.

So you think the LWB swingarm is ok for normal road use?
What about the frame itself?

Of course; every bike after 1973 had them, with few exceptions...

As Bamboo said, I would just look towards a monolever or paralever for inspiration in welding on upper shock mounts to the frame. The single mono-shock upper frame mounts seem to very rarely suffer any failure except on the most heavily abused bikes, so if you make two of them like that then I would bet you would be fine. I also don't think the frame itself would require any reinforcement, again, the monoshock frames don't have anything extra in that regard and they do alright- spreading the load to twin shocks and mounting it in the same spot as the mono's but mirrored should reduce any need for bracing.
For the swing arm, as Seth said, the direction of force will changed a bit. I would imagine a pretty basic beef-up of the lower mounts, spreading them further for and aft for example, would suffice. It might be an idea to do as HPN seem to do and make the lower shock mount on the actual swing arm rather than the final drive. Again, just look towards the monolever swingarms for inspiration.

Does a swingarm from the 70ies and 80ies fit on the old /5, driveshaftwise and so, or is only some (then which)? id like to have a longer swingarm, rather than the normal short swb swingarm.