If you had a bare shell with mint bodywork no rust, a recent respray and fully under sealed and wanted to build a very fast road car and occasional track car for 20k what spec would you go for?

I'd spend around 5k on making the Coupe look REALLY good, get it to about 350bhp and make it handle well.

Then I'd spend £15k on a bike-engined Westfield

TBH, I reckon after about £10,000 spend, you're simply increasing the quality of components in return for an ever-decreasing gain. For example, the cost of getting to 350bhp is (say) £3k. The cost to add another 50bhp is disproportionate at another £5k. To reach 500bhp is going to be another huge spend AND the sad fact is you won't be going THAT much faster than the guy in the 350bhp Coupe

The Coupe is a great way of going quite fast, quite cheaply. However, its a flawed (FWD) and very expensive way of going very fast.

However, if you really want to spend £20k on a Coupe, I'd suggest:-

2.4 conversion, with something like a GT35 series turbo
Professionally ported / flowed cylinder head
A standalone ECU and a week of Leighton's time
Proper limited slip diff in a strengthened gearbox
The best suspension money can buy (AST / GAZ / Tein, possibly with magneto rheological dampers)
Big brake kit (6-pot calipers and floating discs) and 17" lightweight wheels

There - that should get rid of £20k...

I would go somewhere around 400bhp engine and as Nigel said spent the rest to best suspension and best brakes and some light wheels! Yes and make it look sexy

Could do a 4WD conversion for it too?

Alex, just ask Rob on here(ktm450exc).

He has just received his completed 2.5 conversion with HUGE spec.

I'd say forget he fiat and get a better base car.

Stick another engine in the back. Tune both to 350bhp, and enjoy 700bhp and four wheel drive. The sound would be orgasmic.

I'd cash in the shell and buy an evo 8 for 9k spend 10 k on insurance and dirty women and 1k on Viagra :-)

I'd change it to a 16vt