I want you guys to get a couple of cans of POR-15 and do the undercarriage in it.
Blows Waxoyl and other products into next week.
It's not cheap, but hopefully there is a UK distributor for it.
Here's a link, check it out.
POR15, Inc. - Stop Rust Permanently - Repair Gas & Fuel Tanks
The other thing I would do is install a wideband O2 sensor on that thing so that you can see the fluctuations in the AFR.
Time for a rolling road session and remap?
+1 on the driver weight reduction, Lord knows that I could use an improvement on my own power to weight ratio!