It's actually pretty easy, though I probably wouldn't build an exhaust manifold. There are too many good ones(Speedway is one seller), even for Pinto engines to fool around reinventing that particular wheel. If it needs to be modified a bit, then you can do that easily. You need a MIG or TIG welder, a length of steel exhaust tubing and a selection of mandrel bends from some seller like Summit or Speedway. Stainless would be from another as mentioned above. Then it just takes time.
This is mine at the 'H' pipe forward:
....and from the mufflers back:
Had I not used the '32 tank, would have gone over the rear axle instead of below.
The only parts 'pro' made were two pipe fittings that instead of butt welding on the 'H' system, were expanded at a Midas for coffee and donuts for the shop help($5-$6)
Time to make, total - probably 20 hours or so.
Cost - about $100 for the bends and a 10 foot length of aluminized exhaust pipe and the SS clamps