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As long as you keep within the same revision you'll be fine. There is four (five) revisions of the bh/be chassis - A, B, C ,D (E Australia Market). A/B/C should all be compatible, whereas D(E) has slightly different geometry around the lights. Rev D was produced from mid 2001 onw ards - I have a revD BH5
Rev A/B/C look like this:
Rev D looks like this:
There are also minor differences between rev A/B/C mechanically. Many people liken the rev Ds to a completely different setup mechanically, especially around the twin turbo operation