If you are thinking of getting a new Brooklands style exhaust made it may be wise to look at a better design for the internals, rather than copy the rather poor design of the original. The shape of the Brooklands system should mean that the internal pipes are one above the other, not a perforated diagonal joining the two. This may be part of the problem with the system? The "final" Brooklands upgrade does seem to have fixed the cracking problems and is worth looking at if you are fabricating a new system.
