As much as anything it is the responsiveness of the Mikuni's which people find from them. I know the Webers are the same but the Mikuni's seem to provide more from what I have read.
Exactly what model of Mikuni's they are I am not sure - they are from a Yamaha R1 of the carburetted version and pre electronic ignition and these are the ones which are recommended for this type of application.
The Djet with Megasquirt was another option but at the moment it is a question of getting it running well on the SU's. It had Strombergs when acquired on the cast inlet and exhaust manifold. It now has the aluminium inlet and FI twin exhaust.
Re the pistons no I bought them a long time ago when it seemed like a good idea.
The SU's are HS6's - I have a pair of HIF6's from a V8 Rover but they do not work correctly for this application.
The head has already been worked extensively with double valve springs and opened up ports. The valves are bigger than normal, the stems of which are thicker than the valves on the 74' B20E engine I have. They may be ex Holden's. The car is a 1970 142S which supposedly was one of a group which were modified at the same time. It includes a GT dash and a Mota-Lita steering wheel which appears to have been on it from new. The floor is covered with rubber, with carpet over the transmission tunnel.
The gearbox is an M40 but I also have a 5 speed Type 9 Sierra gearbox which was also used on some US 4 cylinder Fords. There is a conversion plate made for them and available from the US which enables the M40 bellhousing to be bolted up to this gearbox. This a longer term modification.