The XJ clocks are an relatively easy modification to the chrome bumper MGB as they are both of the 4" Smith's design. The clocks pictured below are off an XJ6 4.2 litre 1976 model.
Jag XJ6 4.2 Clocks
IN FAVOUR OF CONVERSION
SPEEDO - Most should be 1,000 turns per mile. Same as the standard MGB. If you have an V8 LT77 gearbox the speedo output is set up for a 3.07 rear axle. So as long as you have the MGB V8 axle (3.07) the speedo should read accurately. If you opt for a Jag IRS conversion ratio's of 4.55, 4.27, 4.09, 3.77, 3.54, 3.31, 3.058, 3.07 and 2.88 are available.
SPEEDO - Range goes up to 140 mph instead of 120 mph on the standard MGB, much more suitable for a V8 (V12 Jags had a 160mph speedo)
SPEEDO - The trip counter reset on the Jag clock is on a remote cable, so can be mounted to suit. Later models have a reset built into the face.
SPEEDO - Cable fitting is the same as the MGB, and comes with a removable 90 degree angle attached as standard if required.
TACHO - Being a 6 cylinder the correction is less for conversion for 8 cylinders. Zaks method of adding a variable dashpot to pins 4 & 7 works on this clock to. A V12 tacho would require an adjustment in the opposite direction which is not covered on Zaks site.
TACHO - Rev range is lower on the Jag tacho, redlining at 5,000 and topping out at 5,500 rpm. Suitable for a mildly tuned V8 and gives the impression of a freer revving engine. For more highly tuned V8's the V12 tacho goes up to 7,000 rpm
BOTH - Wiring connections and internal light fitting are the same.
BOTH - Beautifully back-lit in green.
BOTH - You don't loose the nice chrome rims as these just transfer over to the Jag clocks replacing the matt black ones.
BOTH - Cheap conversion, my pair cost £5 each.
You gain an internal demist light with the Jag clocks, which means you can wire it up instead of that horrible white light mounted in the radio console.
AGAINST CONVERSION
BOTH - Have to drill out spring mounting horns from both sides of clocks and copy MG mounting setup using thin long nuts and bolts on rear of clocks.
BOTH - Have to remove both Jag indicator lights, and replace with MG ignition and high-beam ones, simply pop out the old and pop in the new.
BOLLOCK-UPS I MADE
To remove XJ clocks simply push the clock in and twist, don't half destroy the dash like I did.
To remove the glass retaining rim and gain access to the inside of the clock, twist and pull, don't start prizing open the claws.