Just took my rolla for trip from Brisbane to Melbourne and back, and just noticed my intake manifold was cracked. I have a spare 5k manifold, but ive noticed the ports are larger on it. Would i have to port match on the head to use it or do i need to find another 4k one?

Port matching would be better. Make sure you have the new gasket first, get a one-piece one from Unipro or similar, and match all three diameters. Its easy to carve the head out with a tungsten burr, you only need to go in about 20mm and blend the enlarged hole down to the original size. Finish it with a flapper wheel.

https://www.carbideburr.net/carbide/sc-6-carbide-burr-die-grinder-bit/

If you don't it will still work, in theory not quite as well as the sudden step creates a  lot of turbulence. Of course this might affect the peak rpm badly, but be better at lower revs, who knows?

There's a photo in here of when I did mine, you can see the rags stuffed down each port to stop the swarf going everywhere.

https://www.rollaclub.com/board/topic/42407-the-girls-ke70/