Very good question, if I'm understanding it right.
Up to now I have used a double wishbone layout <snip> I am now looking into unequal a-arm layouts
You're aware that "double wishbone" and "unequal a-arm" mean the same thing? Since the '30s "double wishbone" implies non-identical wishbones. The only application I can think of where equal a-arms (or equal wishbones) makes any sense is 2F1R trikes.
My main concern here is keeping the bump at minimum.
When most of us tinkers are designing 2F1R, our main concern is keeping the CG inside the lines joining the tires' contact patches, and with relatively high CG vehicles like yours, that means minimizing the risk that the rear wheel will overtake the front wheels. With modern high performance street tires, I think it's unlikely your trikes would get through a quarter of a spin before they flipped over--I'd think your main concern would be avoiding oversteer, and...
...maximizing our cornering adhesion characteristics...
...is not going to be the same thing as maximizing your cornering adhesion. Ideal "characteristics" are those that leave the operator on the trike (rather than vice-versa) and in control, and an imbalance of front wheel adhesion vs. rear wheel adhesion could compromise those characteristics.
Since you tell us your trikes already...
...out corner the native pre-converted units by a fair degree...
...perhaps you should tell that to everybody else too and leave well enough alone, performance-wise. Equal length a-arms (wishbones) promote understeer, so your current layout is probably enhancing stability. It offers the same benefit as the original Morgan three wheeler front suspension (sliding pillar) in keeping the camber angle of the front tires equal to body roll, and thus equal in camber to the rear tire, which makes the vehicle more predictable when one gets into the spooky stuff near the limits of tire adhesion. Since you can't improve camber in the rear, think twice about improving camber in the front; you risk having a vehicle that "lets go" in the rear faster than the driver/rider can correct.
I am unsure if the inclusion of negative caster during body lean will translate into a legitimate increase in cornering proficiency.
I think it will demand
a legitimate increase in cornering proficiency. I think your riders will need to be more proficient than they need be with equal length a-arms/wishbones (or control arms, as they're commonly called on automotive design/discussion sites such as this one). Were I to license your design, I'd be more interested in how normal people handle it on normal roads than in how racers handle it on racetracks, and I think other potential licensees will feel the same way.
I welcome any and all advice.
Robert Riley's book Alternative Vehicles for the 21st Century
would be $49 well spent. He has extensive and well illustrated explanations of three wheeler dynamic stability. Were I you, I'd pay particular attention to the areas where he disagrees with you about trike design...they're too many to list, but the 2F1R/1F2R--understeer/oversteer issue is one of them.
[EDIT: I googled it. http://www.rqriley.com/alt-car2.htm
2nd Edition, Published by Society of Automotive Engineers (Oct. 2003)
SAE Stock Number - R227]
Locost builder and adventurer, and owner/operator of http://www.kineticvehicles.com