Using twin DCOE Webers might cause a standing pulse in the airflow. The su carbs use a balance tube on the intake manifold for this exact reason. Just re-jet the SU's and moving your timing to a maximum advancement no more than 32 BTDC. If you don't already have an exhaust extractor header for the exhaust, get one. This will put a low vacuum to each exhaust valve opening before it opens and allow for better breathing thus allowing the camshaft to work it's magic. It's not just about the intake when modifying. Inhale - Exhale. :)