I'd certainly sign up for a go in one 
Which reminds me.. one day I ought to ask you if I can try the MX5 on for size (if you turn up for a curry in it). Always wondered if I'd fit (I'm pretty sure I already know the answer when it comes to Westfields so no need to ask there!
)
No problem at all. Well, I say that. It's actually Emma's car.

But.. I think if the MR2 was OK you'll be fine. The transmission tunnel is not anything like as high and wide on an MX5 from what I recall.
As to the Westfield, there's always the central steering column conversion and a buttock on each seat option if you can try not to think about where the propshaft would run.

I'm sure I threadlocked the diff UJ bolts.

Yeah, It'd be fine.

Speaking of which, if we're talking about silly power to weight ratios, my mate has a cossie turbo in his westfield and north of 400 BHP. They've been built with 6 litre+ V8s before as well. This is in a 650 kg car (well, maybe 720 with a V8). Even that sort of spec is far from undriveable. OK, the situations in which you can give it everything get less common, but you can still use the performance that that sort of power to weight gives if you're careful. .. and you can easily kill yourself if you drive like a teenager, of course.