Need help fabricating exhaust manifolds

[aerosam]

Hi guys,

One of the last big jobs on my to do list is to fab the exhaust manifolds, so far i have welded the exhaust flanges on to 10" lengths of 2" dia, 3mm wall pipe.

At the moment I have 4 straight pipes sticking out of either side of the engine. I planned to join them all together by welding in another length of 2" pipe across the open ends, but that means I have to cut 4 2" holes in it to allow them to fit snugly, how do i do that?

The rest of the exhausts should be fairly straightforward, it's just the manifolds I'm struggling with. I'd love to be able to buy a pair of ready made mainfolds, but they just dont exists for my engine (BMW M60 V8) and i can't afford to have bespoke ones made for me either.