I recall reading, most likely in the E-type Haynes manual, that a “useful dodge” is to flip the cam bearings 180 degrees, since the upper shells take almost all of the load and consequent wear. I still prefer to change them out with new. They’re not expensive.
I stand to be corrected but I am under the impression that the rule of thumb is 0.001” of bearing clearance per inch of journal diameter - though that might be specific to crankshaft main and big end journals. If it applies to camshafts, which in the case of XK engines have 1.00” journals, your clearances might be a little loose. I haven’t plastigauged mine yet so have no real comparison to go by.
The manual says permissible clearance is 0.0005 to 0.0020.