Well, header is 1.5 but do not go for end can of 1.5. Go for 2 1/4 and weld adaptor on header or link pipe. I did that using Benelli Tornado tre can and happy with results Why? Because 1.5 cans are not ideal volume-wise for huge mono like DR. And avoid carbon. Please please, avoid carbon. And if possible - avoid "thin" and "superlight" exhaust. I have collection of photos from our DR colleagues with blown to bits supertrapps, carbon exhausts etc. - DR pulses are too much for carbon. Try to get stock exhaust can from laaaarge displacement sport, sport touring or roadster bike. One of finest ways to go - make and Y-link pipe and buy couple of oval stock aluminium end cans from Ducati Monster 900+. If you do that - I bet your bike will sound beatiful and engine will breathe OK.