Well, it should fit if you take the connectors under the wheel (and all the way to HU connector) and transfer them to bravo as the bravo one doesnt have enough contacts. As for aftermarket radio, you need a box (like http://www.celsusice.co.uk/product_details.aspx?product_code=asc2618) that lets you connect the wheel to converter (made for HU, JVC have their own etc), that transforms the signal for the new headunit.
I couldn't say with any authority if the wheel itself would fit, but I'm sure it would. The issue is the wiring. Make sure you get a wheel with all the wiring intact and feed it through to behind the HU. Once there, you will see it has a mini ISO connector that will fit straight into the remote control socket on the rear of the factory fitted Grundig unit. To use it on an aftermarket HU, you will need an adapter made by Autoleads. The adpater you need is the PC99-X28 for the Marea wheel. This is the box of tricks that does the converting. Once you have that, you need the patch lead to go to your particular brand of HU and the part No. for that is PC99-XXX (where "XXX" is the letters specifying the brand i.e. PC99-SON is the Sony patch lead). Expect to pay about £30 for the pair.
I have had this adapter for the last 2 years and they work a treat. The only issue is that they take a bit more of the precious space behind the HU, but some subtle shifting of looms and some nasty slashes on the back of your hand will get it in
By the way, once fitted, if you have a Bluetooth HU that connects with your phone and your phone supports the Bluetooth AVRC profile, you can control your phone's media player from the steering wheel
Oh, and if you have a Sony HU, I have an old style Autoleads adapter (the 1 piece version...does exactly the same) so let me know if you want to buy it
Rob Mk.2 Marea Weekend 1.8 16v 115 ELX - Bigger IS better !