Doug,
I´m a bit confused. Do you have an 1947 MK1 or a later MKIV engine (in 1947 frame)?
Both models have the aluminium woffle box, but different exaust pipes.
The ex pipes for MKIV are available from Armours or Faked but not the MK1 type (with a different bow shape, caused by the different cylinderheads). Woffle boxes are hard to find and I think there are no replicas. On MKIV was also the option of to use the normal barrel shape chromed silencers, also available from above dealers.
Michael