Cheers for your help dragracer,
after reading your thread I thought this could be the way to go so I purchased a complete
Suzy back end arm , wheel, brakes, master and caliper , pedals etc complete yesterday from ebay for the same price of just buying the chrome moly to make a swing arm, $225..............bloody bargain 
Glad i could be of some help Johnno. I hope our original poster can find some benefit to this as well. Used Katana parts are plentiful and very cheap here in the USA. Those bikes were the bottom tear of the sport bike category in comparison to the GSX-R and got no respect although they were very good bikes in my opinion.
If you can buy the upper shock mount off the bike, i would suggest you get that as well. It will help you in setting up the upper shock mounting point- just extend it on each side to match the frame width and you're done. Please remember what i mentioned in one of my posts about the lower center stand cross brace. This part will fail if you try to use the original steel. You must cut this out and replace it with either chromemoly or mild steel and reweld the center stand mounts as you will use these to connect the lower shock pivot to the frame. We were not aware of how fragile this original steel was and found out the hard way. The bike started to bottom out and we could understand why. At first we thought the shock was bad and put on another but the bike still seemed to drag on the rear fender more than when the bike was first built. A quick check while the bike was elevated revealed that the steel brace was multi-layered and was literally peeling apart when we attached the pivot. We decided instead of bracing it up, to just cut the piece out and put in a new one. I pulled the motor out to make it easier for the welder to replace the bracing. I suggest you put in a dummy set of lower half cases and bolt it down before welding as the heat might pull in the frame a bit at the lower rear motor mount. I had to jack the frame out a bit to get the engine back in due to this issue. Not a real problem but i just wanted you to be aware of what i experienced.
Attached you will see a picture of my KZ 1000 mono shock conversion illustrating where the lower pivot is mounted. The Honda will be mounted in the same manner. When welding your upper shock mount to the frame, you need to set your ride height first to determine exact where on the frame to weld in the cross brace. If you are a good fabricator /welder, you can make a plate thats adjustable, up or down, on which to mount the upper shock brackets.
I must apologize again to GONZO for stepping on his post. I'm simply trying to offer my experience on a mono shock set up in hopes of saving any interested party a lot of research time and in particular- MONEY. Lol. As Johnno has shared, you can buy all the used parts for much less than the material it would take to build an arm. Plus its all is compatible if you get the rear wheel, spacers and brake set up. All thats left is welding in the upper shock mount, gettting an offset sprocket and a longer chain. Umm, don't forget about the caliper support arm- modify the Kat arm or make one yourself. Be sure to get the brake line too- assuming you having hydraulic rear brakes to begin with (F model). If not, get the Kat right side Kat brake/foot peg set up and modify those. Don't forget the left one to match
