Would a front bumper for a mk7.5 fit onto a mk7? I know it's a facelift so looks different but the way it attaches to car looks like it should line up from what I can see. 

Maybe not down to the shape of the lights

I think you're right. On closer inspection the lights are shaped differently. Just seen a front bumper with glossed plastics cheaper than what I'm being quoted to get my grille etc sprayed so thought it might be worth a pop. Do you know if the facelift rear diffuser is a simple swap for the pre facelift diffuser? I know the st diffuser fits with different spats 

If you're going to facelift your Mark 7 front-end wise, you'll need the facelift bumper, grills (top and bottom), fog surrounds, headlights (wiring new headlights is one of the hardest parts) and bonnet. I believe the wings/fenders are the same. I'm not sure if it's a straight swap/plug-and-play, if it is, you could always sell your old non-facelift parts to make your money back/reduce costs.

As for the rear diffuser, unfortunately I'm not too sure. Hopefully someone else can clear this up. I know the ST ones can fit if you have different flaps on each consider installed too, as you mentioned.

All the best. :)

Front bumper would need bonnet, lights (remember different wiring) as well for the bumper to fit 

Going for fl look may as well Chang rear lights again different wiring and also change the diffuser with spats at the back and yer sorted 

Not too fussed about the facelift look just want the black plastics, fog grille etc that was being sold with the bumper. I do want the rear diffuser though however that's being sold as a whole bumper unit so is the bumper a straight swap from a mk7 rear bumper to mk7.5 rear bumper. 

If you're swapping the whole rear bumper it would be a straight swap

See my parts for sale on thread "philf1s Spirit Blue Fiesta ST180 parts for sale"