The Fiat 500 is one of the most customisable cars you can buy. If you’ve got a few hours to kill, just go on Fiat’s online configurator and have a look for yourself. There’s an infinitum of options to allow the cutesy city car to blend seamlessly with your wardrobe/favourite lifestyle activity/horoscope.

But one thing the Argos catalogue-sized option list won’t allow you to do is add a carbonfibre widebody kit, rear-wheel-drive layout and drop an Alfa 4C’s engine behind the front seats.

For that, you need to go to Gran Torino Engineering. They’ve created the beast in the video above, the Giannini 350 GP Anniversario, the tuning firm’s mad mid-engine rear-drive widebody 350bhp Cinquecento built to celebrate the 100th anniversary of the famous historic Italian tuner Giannini.

Starting with a normal Abarth 500, Gran Torino strips pretty much everything out of it, then stuffs it full of goodies until it looks like the four-wheeled offspring of Mr Creosote.

It’s not just a 500 in a fat suit though, as one of the most drastic changes is the engine. The donor 500 Abarth’s 1.4-litre turbocharged four-cylinder was thrown in the bin and replaced by the 1.7-litre turbo-four from Alfa’s two-seat, carbon-tubbed 4C sports car.

Now residing behind the front seats and good for 350bhp (up from its 237bhp as standard), its power is fed to the rear wheels via a manual gearbox. But, if you want it, you can also spec the same six-speed paddleshifter from the Alfa.

It doesn’t stop there. The 350 GP has also been blessed with drilled and slotted Brembo brakes with six-piston calipers up front and four-piston calipers at rear. Then there’s the visible in-board Ohlins shocks, peeping out of holes in the car’s hood and rear hatch.

The massively bloated widebody kit is made of carbon and features new air intakes, hood, modified grille with fog lights, rally-style roof-mounted wing, and all finished with a set of 19-inch forged alloy wheels.

Apparently, 100 units of the 350 GP are set for production priced from €150,000 (RM750,600). So if you want one of the maddest 500s around, you now know where to go. If you’re not tempted, just embrace the madness in this video…