I did double check those measurements. I am a trade certified fitter and turner with 20yrs plus experience, not a 14 yr old hairy arse with a school ruler.....Other housings and diff heads may be different but my combination is fine.... The diff head came out of a 84 1.5 ZX Californian Sunny and I have always assumed it was a H150. By the way I was measuring from the inside face of the mounting flange to the centre of the spider gears and all the diffs I have measured the same. I also slapped an axle in the hole with the head on its side to load the spider gear and compared things that way too.