The only way I know you can do that is to get a Spirit 1100. The difference between the bikes is in the transmission...not the rear-end. I am not aware of any alternative gears for the Shadow shaft drives. Someone else might...
A couple of months ago, someone posted a link to some company that
was making gear sets for the shaft drive bikes.
I didn't really pay too much attention to who posted it or what the site
was...so I can't really say what specific bike they were for, but they
were for a version of the Shadow.
Maybe whoever posted that will see this thread and repost that site.
I know a little about the rear gear stuff for the shafties.
The gear ratio is 3.40 but other "model/s" in the Honda line will interchange. Most that I know use a gearset(only) from the V-4 Magna's which are 3.18 to lower the rpm's. Otherwise the people are looking for a cheap stock replacement gearset (3.40's).
A guy on the V-Four Sabre site(www.v4hondabbs.com) (Dave Dodge) has these gears AND will do the install to your final drive unit. I think he also will swap units....just not sure. He's got a website but I can't find it right now. Asking the V-4 board people will get you to him.
Sometime ago I replaced my final drive gear set and the price for the gear set was $238.00 and that wasn't counting the cost of the "seals and other associated pieces" needed for replacement. So it's quite expensive IF your on a budget.
I know the 3.40 ratio is what the 1984 VT700 had as a final drive so I assume other similar models would be the same.
I'm looking at manuals that are showing a final drive ratio of 3.091 (34/11) for 1100 Shadow models, at least the for 1988 and 1995-2004 model years. So I wonder if there was a change somewhere in between?
I have a list of Honda model/yrs for the 3.40 gearset. Most of the gearsets are in the V-4 Sabre's models (700/750) and differing years for the Shadows and a few years of the CB700S NightHawk inline-4. Only 1 year for the V-4 Magna (3.18 gearset) because they used a different housing on that year (1982).
If it's not too much trouble, I would be interested in the gearings. I've got four different manuals I look at, but no guarantee mine are correct, so I would like to note any differences.