71 Dodge Dart Swinger in England

Hi Guys, back from our USA holiday 1500 miles around California and Nevada. Awesome country I must say! Anyway whilst there picked up a B&M flex plate and a new transmission mount. I have an engine vibration in neutral, see separate post .360 engine vibration
However I also have a diff oil leak so thought I'd start at the rear and move forwards, so I stripped the diff out thinking it was a 8 3/4 dodge item (bought gasket ready whilst in USA) turns out to be a 9" ford unit???WTF!! Is this a known upgrade? Also I think the prop is too tight as there was zero movement to slide the yoke into the 727 trans? car is on axle stands under the axle.

So starting at the rear I will sort this first, check prop length, yoke play and then move back the the vibration issue. I'll post photo of the diff housing and axle tomorrow.