Easiest distributor to modify for the 226/254 is the flathead 6 Chrysler, Plymouth, Dodge with centrifugal and vacuum advance. It fits into the block hole with no machining. The stock Ford clamp will work. All that neeeds to be done is to weld the splined Ford drive onto the the end of the Mopar distributor at the correct length. It already has a good flathead advance curve. Pertronix makes an electronic conversion for it. Millions were made from the 1930s to the middle 1960s. The 200 Ford distributor is the next best bet. The part of the housing that goes into the block needs to be turned down and so does the drive gear. The drive spline from the flathead distributor must be welded on at the proper length. The centrifugal advance curve is too long and must be redone which means partially dismanteling the distributor and shortening the advance notch on the shaft. Some are stamped 10 degrees and could be used as is with 6 to 8 degrees static. Installed, it looks real stock and con use the original distributor cap. Also possible are c***y 194/230/250/292 six cylinder distributors. They fit into the block but not all the way without shortening the distributor drive gear and would need the Ford spline welded on and the advance curve shortened. The 200 Ford and c***y six distributors both come in electronic ignition versions, points, and pertronix is available. To use the vacuum advance for better part throttle economy would be a cut and try type project. My opinion, is that anything with a proper centrifugal advance curve is better than the stock all vacuum advance distributor.