Howdy,
Yes I considered then dismissed the NA+T option.
What i'm really looking for is a cost efficient and reliable base engine to build on. Given the relatively unknown nature of the car and it's slightly dubious history, I wanted to start with a clean slate so that I know that it's a) Reliable for me b) If I ever come to sell it, i'm not passing on a grenade. Karma's a b*tch at the end of the day. So I was facing an option of buying, then turbo'ing another 2JZGE (£400+turbo parts) then always having a semi skimmed turbo Supra (no offence intended to any NA+T drivers out there) or doing something a little different yet well proven. The end goal will always be to end up with some sort of forced induction setup on the car. However, i've learnt from painful previous experience that the only way to do projects like this and not have them turn into Craig Charles's post vindaloo chamberpot is to do it in manageable stages that keeps the vehicles off-road time to a bare minimum. Or for any Agile/Scrum developers out there, Ship Early and Often.
I might actually write a side article on Agile car project execution :-D
In the meantime, I acknowledge all your concerns on the W58. It's not the worlds strongest box. Looking at it, it reminds me a LOT of the small casing Nissan box. I've lunched in the region of 20 small casing Nissan boxes in my time :-) I've installed some high impact gear oil + a sprung plate. As part of the engine swap i'll also remove as much lash from the drive train as possible. Hopefully this will keep it in decent shape while I figure out which transmission upgrade options are right for us.
Glad you're enjoying the read and thanks for the questions and feedback.