At the drivers briefing we discussed that it was OK to smooth the weld out on the exhaust manifold ports as the welding could be very variable in quality. We agreed that as long as the ports were not enlarged they could be smoothed to the original diameter of the pipe. So I purchased a second hand manifold off eBay and have used a rotary tool with some cobalt bits to achieve this. It is recommended to braise around the outside of the ports to maintain strength so I need to find someone to do this locally for me.