Yes, I was aware of the Puma - it wasn't a direct copy in terms of the mouldings, although the original late 70's GTV did look like a Mk1 Nova.
The later cars went to gull-wing doors and as Sudaddict correctly points out, had the Alfa 1500 and later the 1.7 16v fitted to the VW gearbox via an adapter plate. In fact, from what I can make out (my Italian is not great), a Puma GTV 033 even won a race, when it rained on the grid and all the other competitors spun off
The GTV driver would have been very familiar with tail-happy driving, so kept his cool to take the win!
I still stand by what I said about the VW gear ratios - I have 15" wheels and 205/60 rear tyres on Green Machine and with my old 3.889:1 final drive the acceleration was no quicker than an equivalent Alfasud (0-60 in around 9-10 seconds). Even with my current 4.11:1 final drive 0-60 is probably only a second or so quicker, and I am still geared to top out at 112mph in 5th. Ideally I need an even lower final drive ratio, like a 4.5:1.
Good luck if you do decide to go the Porsche route Lee, there's not many engines and gearboxes around these days, and they will be expensive. You need to convert you rear suspension to IRS if you haven't done so already, and expect to have to modify the rear bodywork even more to get that flat 6 engine to fit. The end result can be a very fast car though.
You are right - I do enjoy the attention my car gets. But you will get the same attention no matter what engine is in your car