The numbers mean nothing to the best of my knowledge (might be wrong), but in 1964 there was only one converter for the 904, 11", narrow ring gear, 1.550 pilot and of course 18 splines. It is used on all engines, leaning tower of power and V8's. The #403 might be the rebuilders part number, but I can't say that for sure. It's been rebuilt for sure as the factory never painted converters. Hope this helps.