My reading of John's post is that he has a Dunstall 810 barrel for a 750 Norton. Not a Dunstall 750 barrel, which is much less common than the 810. That's why he's looking for 76 mm pistons.
For pistons, I don't know of anyone that carries 76 mm pistons for Norton twins as a standard item. You can use pistons from other bikes (Harley, Kawasaki, Suzuki), but they all require some machining, either honing out the rod for a larger pin, or machining the top flat and cutting valve relief notches, or both. If you really want to keep it at 810, you might consider talking to the aftermarket piston manufacturers (Arias, JE, Wiseco, etc.) about making a set. I've had custom Norton pistons made in the past by Venolia, and currently have a variety of sizes made by in batches by JE (sorry, no 76 mm so far). They are a bit pricey for a single pair, and you probably don't want to do an order for 8 (four pair), which would get a better price per set. I've thought about having some made, but didn't think there would be enough demand for them, particularly given the reputation the 810 kits have for failure.
If you just want the Dunstall look, consider having the cylinders sleeved to 73 mm so you can use standard pistons.
Ken
