If it has the brass nuts holding it onto the manifold you should be able to get away with keeping the studs. Even if the studs are a bit bare you can double up on new nuts to get some purchase.
I had a nightmare getting the first britpart front pipe through the crossmember without it hitting the floor and jamming. Eventually I had the whole car jacked up over a kerb to give me the height.
After two years it was shot and so were the studs.
I ended up putting a SS stainless one on but this time it fell on with a standard jack up and axle stands. No idea why.
I couldn’t get the studs out with not having oxy so I drilled the sods out and fitted some stainless nuts and bolts.
If you take the manifold off be prepared to struggle getting the studs back in. I still have the centre one missing