Just a quick search found this.
Quote:
|
It has to be a period 289, and roller rockers aren’t allowed for Appendix K, though the standard rockers break at 7000rpm so you need to invest £1500 in a hardened set. The standard Hi-Po cast exhaust manifolds must be retained but the exhaust is free from there back. Top-running cars enjoy over 400bhp, but it costs – Steve Smith says the best motors run out at £18,000
|
I'm also curious why you cannot use the Mustang HiPo option Try Y headers.