Hello, I currently have a mk7.5 1.25 and looking at converting it. The st conversion would be the goal but I wondered if the 1.6 engine is a straight plug and play? If not what would I need to change to make it fit as this would be cheaper than the st conversion?

The cheapest way is to sell your car and buy an ST.

By the time you've bought the engine, gearbox, turbo, ecu you're talking around £2000. Then there's other bits such as driveshafts, intercooler, intake, exhaust and possibly a clutch that you'd need to buy.

So by the time you've spent £2500 to get the engine bits, you've then got to spend a further £1500-£2000 on the ST diffuser, side skirts, front bumper lip, spoiler, front grill, seats and I'm sure a couple other bits i missed. So for a full conversion I'd guess at nearly £4000? That's if you do the work yourself. Expect way more than that if you're going to pay a garage to do it.

All this work for no gain in resale value as engine swaps/replicas will never make the car worth as much as an actual ST. Btw a fiesta ST can be had for way less than £10,000 nowadays and I'm sure you'd get at £5000 trade in on a 2017 fiesta. Surely that seems a lot less hassle than swapping an engine.

Yes, got to agree with Luke there. Plus you'd have the hassle of insuring a modified car.