the front to back distance would be measured with the rear ujoint loose just like you were first installing the driveshaft (& that is a good time to check that) when you butt it all the way forward to clear the rear yoke then move it back to seat into the yoke, that distance. Right now the side to side slop the front yoke has in the extension housing bushing you mentioned, 1/4 seems like a ton or did I misread something.