Build suggestions for 340?

I think you may want to figure out what you're going to do with your heads first or at least along with all the other decisions you will be making. As much as I love ironheads I ran ported X's for 30 years it is getting harder and more expensive to have good machine work done. If your heads have been done fairly recently and don't need a complete rebuild then I would go for it. but my finding was by the time I had quality work done keep your( fingers crossed), and quality parts installed I still had a 50-year-old head that weighed close to twice as much. And without any port work produced approximately 15% less power maybe more.