I have never done this particular conversion, but I have hand profiled several hundred custom race pistons to fit combustion chambers on many different types of racing engines. Most of them were for very common engines that have been raced for 20 or 30 years, so you would think that by now they could make a piston dome that would fit the chamber. Since the Stovebolt engines aren't your average run of the mill engine anymore, its not a surprise(at least to me with my background)that you are having this issue. One quick method of finding out how bad the piston dome interference is, is to get a stock flat-top piston and put a bunch of modeling clay on top of it and rotate it to let it form its own dome and impression of the chamber relative to the piston, then compare to the new Venolia's you have. Put a light coating of oil on the top of the clay so it won't stick to the head. You will then see really how much massaging needs to be done to actually make it fit the chambers.
What you might find is that the real culprit is a really poorly machined head or cylinder bores relative to the head, compared to a set of pistons that are machined with much tighter and closer tolerances than a 50+ year old block or head.
