Topic: Swapping out speedo/tach gauges.. what do I need to look for?

[1976HondaCB550F]

I want to swap out my stock speedo/tach gauges with something smaller and possibly more "rectangular" like.  The stock gauges are the highest point on my bike and I want to lower that profile.

What do I need to look for in a replacement in order for it to match up to my '76 550F?
I dont know enough about the technology yet...

I like the idea of a single unit cluster like the newer sport bikes but I know they are different technology.

I've seen a handful of those "mini" tachs for Harley's on ebay, like this one...
Those shouldn't take too much modification of the existing wires and cables, no?

I know people have used generic digital tachs, like these..

http://www.cbxmanmotorcycles.com/Standard-Tiny-Tach-Tt226nr-2c-Digital-Tach-Hourmeter.aspx

What are some ideas others have done?  What do I need to keep in mind when looking for something that'll work without too much modification?

Thanks...

[robdrobd]

I'd like an answer to this as well. Thanks