I would also recommend the positive viton seals. If you’re running aftermarket 1 piece valves, they do not have the second notch for the factory o-ring. So you would be forced to convert to viton seals. You can even do the machining yourself with this tool:
https://www.summitracing.com/parts/hrs-92040
I bought the comp version, but those went up quite a bit in price. They appear to be the same, however.
I do have a question for you though, I have a set of 143 heads on my 326. Can’t find any real numbers for combustion chamber volume, have you had your heads cc’d? Thanks