Talk to Kenny Coleman at Engine Data Analysis (EDA) in Castleford Yorkshire UK.
Engine Data Analysis "Specialist Engine Buiding & Tuning
He builds many genuine GT40 289 motors which use ported cast iron heads. He gets 420 bhp on webers on his accurate dyno from 289 race motors. These are race motors and not really driveable on the street. Kenny is very knowledgeable and has been building every sort of V8 engines for street, race, drag racing etc for years. He has just built a 347 Ford smallblock for Martin Gough which we saw being machined, balanced, built and dyno tested - very impressed with the quality of build and excellent results.
Cheers
Mike