While it's possible the gasket won't be ruined, I'd sure want to have a new one available.
But I have to say that the ones I've cut by hand from "high temp" roll gasket material seem to last just as well as the machine cut ones.
The individual gaskets are available from TRF, tho, as you can see in the drawing TDSkip posted, there are different gaskets depending on whether you have an early low port head or the later high port.
Also, if the studs that link the intake and exhaust manifolds together are still in place, you'll probably want to remove the exhaust manifold from the downpipe as well. Which means you'll need that gasket, and possibly new studs & nuts.
Easier possibly, to leave the manifolds on the engine and just remove the carbs and linkage. But you'll still most likely need new gaskets for any joints you disturb.
I also replace the lockwashers almost every time, as they lose their 'spring'. If the ones that come off are noticeaby flatter than new ones, they should be replaced. And although not original, I've found that a heavy flat washer on the outermost studs (between the lockwasher and manifold) seems to help with sealing.