[xj-s] Warning: cooling fan clutch/fan compatability problem

While renewing the cooling system on my '92 XJ-S, and suspiciously eyeing
the radiator fan (small cracks at the front of the hub) and the clutch
(heat level rises in heavy traffic), I decided to renew the twain, and (to
avoid aftermarket compatibility problems) ordered a new fan clutch (Part
No. EAC 4751) and a new fan (Part No. EBC 4553). I ordered each from the
cheapest supplier, figuring a Jag part is a Jag part.

Wrong. The fan is clearly the new black-bladed one described in The Book,
though the metal dished hub is replaced by a flat metal hub placed further
back. However, the new clutch I received does not mate with either the new
or old fan, apparently because it is larger in diameter than the old clutch
(new clutch: 7 1/4" diameter; old clutch: 6 5/8" diameter).

The new clutch is clearly an aftermarket unit, as it has slots instead of
holes for the four bolts (and also, under the “EAC 4751” label, I can
discern a label reading “EAC 4751X”).

'92 XJ-S Conv. (currently seeking cool)