Technical Suggestion/Help, gauge swap on 81 kz750

I am tired/fed up with my 85mph limit on my speedo gauge, so I got some gauges from, I don't know what year bike, but the new to me speedo has a 140mph top speed and no stoopid 55mph indicator (yeah!).

so. . . I am trying to figure out what to do, either gut the gauges and swap the internals to keep the same outward configuration on the existing gauge cluster so everything mounts up correctly or keep the gauges in tact and modify the frame and lights to retrofit the "new to me" gauges to the existing 81 cluster.

I am leaning toward the gauge cluster frame modification so I don't have to open up the gauges themselves (but I am missing the gauge baskets for the new gauges, I will have to order them or find them at my buddies shop).