Thanks Guys,
The block seems to be sitting too low in our tub. These engine mounts confirm it. I'm estimating they are around 2" long. The rear bulkhead may need to go up a little or the upper gearbox mounts are drilled too low.
Regarding Mk - IV J6 Comment. Assume you are talking about the steel plate riveted to the Aluminium seat back. Couldn't agree more. The upper steel fabrication going from the rear bulkhead to the sills would help stiffen up the rear, but in torsion there is nothing. I am sure Eric was using the engine and gearbox as a semi stressed member when he designed it.
Regards
Mark Beasy