How do we go about fitting an XF 4.1L Weber Carby? Straight in, or modifications required? (1990 Magna TP Sedan Astron II 2.6L)

You will need an adapter plate and to stop it overfueling you should change the jets in the carby.
Apart from that it isnt meant to be too hard.

Nice, after that I'm hoping to get these mods on too: CAI, Exhaust system, mild cam, lower it with superlows

Sounds cool, keep us up to date :)