To me its very basically done and in my pipe fitting experience , gaining flow in industrial use and having to keep swirl and obstruction for metering etc , this is a shit design for gas flow. I see its compact but that mani would be very cheap or SHOULD be considering it is crappy.
Get the flanges , mock up an original mani to show where you want it to go in a jig and put the flanges on in place then run some bends and tube to fit with reasonable flow. Yes , takes a long time if you don't have piping experience. The difference of a novice and a pipe fitter is usually the job gets done , the novice gives up with tons of scrap....
Get a local to make you one , look online at welding sites , teach out to a Pipey.