Depending on power output, maybe no point in two carbs and more hassle to setup.

And n/a carbs can be used or modified to a degree, but the proper turbo'd version is better as the dashpot chamber has a proper seal on it.

Burlen do a lot of SU stuff, but I'd doubt there is much support for the turbo carb

http://burlen.co.uk/

Or maybe Avonbar etc

http://www.avonbar-racing.co.uk/

But Metro, Maestro, Montego turbo, all carbs are usable.

Could do no harm to ask here too

http://www.turbominis.co.uk/forums/index.php