Here's a totally different plan:
- keep your 8-spd Ergo shifters
- get a 110-74 triple crank (anybody's - doesn't really matter) with the chainrings of your choice
- change your rear wheel to a Shimano hub with an 8-9-10 freehub. I like the Ultegra 6500 version if buying new. The steel freehubs bodies work fine with individual cogs, unlike the alloy freehubs.
- build or buy an 8-spd cassette with the range that you like with the chain rings. If you can't find one you like, build it up from loose cogs. There's plenty of inexpensive 7 and 8-spd cassettes out there.
- and here's the key: Put Campy 8-spd spacers from Wheels Manufacturing in the cassette:
http://wheelsmfg.com/8-speed-conversion.html
I've done this for my wife's bike and it works quite well. She is now using a 12-30 cassette that I assembled from loose cogs.
Shimano cassettes have MANY more variations than Campy, teeth from 11 to 34, and the 8-spd cassettes can be built up in just about any combination you like, despite what Shimano might say.