These wheels are Jaguar part number CAC 4379, and they are 15" diameter, 6-1/2" wide, and have an offset of 28.5mm.  This info is clearly visible to anyone looking at the car; it's cast right on the outside surface just inside of the outer rim.  There is also a British Leyland symbol (fortunately very small!) and the symbol of the wheel company.

The lower photo is of Marty Sullivan's spare, and it apparently has never touched road.

Although an alloy wheel, it actually has a two-tone paint job, primarily light gray with a much darker gray accent.  There is no appearance of bare aluminum anywhere on the wheel.

Note that there is supposed to be a puddy tat face motif in the center of the wheel.  Both of these wheels were being used as spares, with the retaining lug installed through the center -- arguably not correct, it's apparently supposed to be used through one of the lug nut holes.

The original motif for these wheels was a two-piece affair with a black outer rim.  Later design one-piece motifs will fit the wheel, but typically have chrome or gold outer rims, so it would be necessary to purchase an entire set to make them match.

Also note that there is no provision on the outside face for clip-on balance weights.  Interestingly, there is provision for clip-on weights on the inner edge.  For proper dynamic balance, you will need to use stick-on weights either out where they are visible or just inside the spokes.