What are my rear shock options ?

[kebab19]

For my shock conversions I used dogbones with holes 127mm apart which restored the rear to standard-ish height (might lift the rear very slightly)
http://foc-u.co.uk/index.php/topic,8167.25.html  - halfway down the page D. Curzon provides the top-hat dimensions in a CAD drawing
Replacement top bolt will need to be 10m diameter and first 60mm unthreaded for extra strength. High tensile bolts best option, off the likes of ebay.

For your weight you'd be best with a 600lb or even 625lb-inch spring depending on whether you take pillions / do trackdays / carry luggage / ride like a loon.  You could try maxing out preload on the original spring - it would probably be fine for solo use @ legal speeds but not if you're really pushing on