I haven't got any figures for a 12v engine, the only one I know of is the one that Susit has now built by David Carson.
I know of a 164 24v with ITB's which would have been 210Bhp stock but with Jenveys & an aftermarket ECU makes 276Bhp which seems like a reasonable gain.
I guess that will be a 50:50 split between the ECU & the ITB's, junking the AFM & going to the aftermarket ECU will have taken it to approx 240Bhp the rest will have come from fitting the Itb's.