Paul hope your keeping well. IMHO modding the ARP4 would be a step too far, financially and quite a bit of work. It's not just the engine and gearbox, but also dash and ECU (tied to the engine) unless your going bespoke, plus exhaust, I could see this all easily getting to £20+k. If you really want to change then I'd go for a nearly new Roadster, put Williams 6 pot callipers on it and if you like it Suplex rear end(but I have reservations), personally I'd rather spend it on fully adjustable Quantums front and rear and tune to how I wanted it. You'd have a lovely torquey trad. that handled and braked well.
