Just been having a look at possibly doing a pipe tunnel myself. Unfortunately the justengines pipe is 52mm diameter, which means that it is immensely big when compared to the slender 35mm of the Hatori 698 pipe that probuild do. Looks like it is going to be a viable option to make a pipe tunnel to fit the thinner hatori but not the J'en one.

Unfortunately the hatori 698 is £115 when compared to the Just engines £40[:@]
ive got even more saving to do!