I can understand where the 670SA has developed a rep for being lean at WOT.
I’ve only run one on an engine on the dyno, and this was a very mild 455 Poncho making about 325hp…….mid-16’s A/F ratio at WOT.
A swap to one of the shop carbs showed normal A/F ratios, so no weird carb requirements from the engine.
The 670 had stock jetting.
There is a shop in town with a chassis dyno that tested quite a few cars running 670SA’s…….most(all?) of which were somewhere between “pretty lean” to “abort the pull” lean.
Some were cured with jets, others got different carbs.
I’ve seen/heard enough stories about unhappy customers running them to where I can’t imagine recommending one.