If the JTek shiftmate works, I'd use it, as the simplest option.

I don't know about Zagreb, but 8-sp Campy wheels were not that expensive here, the last time I looked.

Many people here can advise you on mixing components. I cannot.

I always try to match 3 things: Shifters=Cassette. Then I relax.

Wheels Manufacturing makes 8-sp Campy spacers for Shimano 8-sp cassettes/wheels. $60

Miche makes 8-sp Campy cassettes, but not to fit on Shimano hubs.

http://www.ebay.com/usr/rutlandleisureoutlet this guy may be able to help.

I've used Shimano 8-sp 600 with a Campy rear wheel and 8-sp cassette.
It worked fairly well (a couple of centuries, no problems)