Thomas I may not be able to help but I am interested in what you plan with the motor. I have a 411 mk2 with a 383 in it and a 412 with the 400 like your mk5. The 383 although largely stock ( manifold , mild cam and standard cast iron exhaust ), it has enormous power and will rev happily to 6500rpm. On the other hand the 412 with tubular manifold and alloy inlet has ample initial pull but runs out of punch over 3500 rpm.
I am told the 400 motors can be made to go very quickly with different pistons cam and alloy heads. It might well be that you put your money into that area rather than new exhaust manifold.
I believe the system on the 412 was a custom built set and are not entirely satisfactory because they are to close to the spark plug leads and also as the engine mounts sag and you turn to full lock they touch the steering shaft.
As I said I am interested in what your plans are as I intend to do something to get the 412 going quicker.
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