If the newer designed three bolt carbs have an improved fuel needle and seat assembly in regards to increasing the amount of fuel pressure that can be run, then that would be a point in favor of the using ‘new’ carbs. When testing the original Strombergs, 3½ psi fuel pressure has been the limit and even at that point, I’ve experienced some fuel seepage past the needle and seat assemblies. I’d suggest hitting some of the other sites such as the H.A.M.B. and flathead forums and getting some feedback on the newer carbs in this regard before actually purchasing the new carbs. The problems with the older carbs are well documented but advantages/disadvantages of the new replacements needs to be researched. It’s too bad Barry Grant has folded as their particular Stromberg carb replacements had some very favorable reviews.