My donors brake m/c has a built in servo.

If i decide not to use the servo, can i just leave it as is or do i need to plug the holes?

You need to remove the master cylinder from the servo, some you can mount seperately, and have the push rod operate directly on mc piston.

As with a servo car without the engine running, the brakes wont work effectively if you leave it in.

Thanks Pete, it doesnt look like its going to be very easy to take it out so i may have to try and work out how to get get the servo plumbed in.

Iv just found ou that the servo is powered by a hydraulic or electric (model dependant) pump, neither of which i have on my new engine

Does anyone have any suggestions?

Brakes on the axles are still the same, push fluid in pistons come out.

Just stick on a regular master cylinder ( I expect what you have will be okay though without the extra gubbins) from a car, I used a new landrover one as it was cheap, works fine with discs front and back.

You XJ40 brakes will have a similar surface area to my 4 pot brakes up front and sierra rears.

Regards Mark

didnt some jags use mineral fluid?if so using regular fluid it would sh*g the caliper seals