To answer both your questions, let me begin with the header. I ordered mine through a company called Bestmufflers.com. link to specific header is as follows
https://www.bestmufflers.com/bshop/product_info.php?products_id=2889&osCsid=d937920970f517982d9992aa3da41091
They are based in Australia, and list a header option for the b1600, b1800, and b2000. I believe they had the header advertised as $275.00 AUD, but after converting US dollars to Australian Dollars, the price was close to $201.16. I was able to source a cheap international shipping rate through a friend in the military, so that should save me some dollars- and either way, its going to take some time to get to me. Some people wouldn't go this far to get a header but I had the money and wanted something that would perform better than stock. (and honestly, finding certain parts here in the US has been a little difficult...but I scored on those hubcaps haha.) The only other parts I wish I could get would be OEM b1600 floor pans. (which I have also found for sale online...in Australia...but seller refuses international shipping.)
Now for the distributor I have noticed that they can be mounted on either side. When I purchased my truck it was mounted on drivers side with coil mounted on drivers side (LH) wheel well. Looking at other engine bays I have noticed them on the passenger side with coil mounted close to battery tray. Pictured below I see that I could mount it either way- but just left mine the way it was. I would assume that distributor rotation could change (i.e- clockwise vs counter clock wise or vice versa) depending on which side of the engine it's mounted- so ensuring firing order matched with the rotation of the rotor would be something to contemplate when mounting and timing.