I’m wondering is it feasible to use simple wheel spacers for rear axle in Mk1 instead of fetching and replacing the whole mk2 axle which is wider. Any advantages there ? Bearing wear / stress ?
And for the spacer thickness - how much is too much for steel wheels ?
I think there is about 3 inch diffrence in axle’s track ,
So say about 1"1/2 inch a side , would a XJ6 rim fit with a 225 tyre
Rim would be 6 inches , and 225 tyre would be close to 8" 1/2 inches wide ! 
I better stick to 185/70 tyres 
I’m just aiming for improved stability and it’s said that Mk2 axle in Mk1 is an overcorrection.
Perhaps 20-25mm spacer per side would be enough
They do say this is one reason Jaguar increased the Track on the MK2 , 