In the USA, Redline Weber, Pierce Manifolds, and Carbs Unlimited all stock genuine Webers, with or without the conversion kits.

The K614 kit is required if you have an automatic transmission, as that's the only one a kickdown linkage is available for. If you have a manual trans you can use either the K610 or K614. IMO the K614 is ideal for either trans, as that one comes with a Weber DFEV 32/36 that can be oriented with the fuel bowl towards the rear and still use the stock throttle cable routing.

IMO the "big" Weber DGES 38 is only worthwhile if you've got a highly-tuned rebuilt engine that can make good use of the better breathing. On a stock engine, it'll just be more of a fuel hog for little if any significant performance gain. Some have said a vendor told them this was a "better, newer design", but I'm pretty sure that's just referring to the Weber DG-series in general (DGV/DGAV/DGEV/DGES), which are indeed a newer design derived from the older DF-series (DFV/DFEV/DFAV) but mirror-image in layout.