What is the best / most popular size pipe for building a t3 turbo manifold ?

i have got 1.5'' sch40 pipe and flanges 12mm stainless to make a manifold from but looking at the exhaust port and the 1.5'' it dosen't mate up well and i don't think forming the cast sch 40 pipe as much as needed will fill the exhaust port hole

NB 1.5in sch40 = Outside 48.26mm - inside 40.6mm (Going to NB 2'' would be 60.3mm outside - 52.5mm inside )

Exhaust port on flange 43mm x 50mm

i could fill and port the edges as this is looking more likely but should i be concerned about the 1.5in not being big enough ?

I have seen on the net in the USA they sell a flange that goes from oval exhaust port but its in mild but wont do one in SS ( dont fancy that as the crappy weather here in the uk ) Link to flange

any other options ?

RHD uk spec S2000

 

man, thats going to require a lot of porting, as well as layers and layers of welding to fill up the space.