As far as I am aware, there are M42 stock chip definitions floating around for Tunerpro, but the proper offsets and checksums are NOT publicly known. The thing is that the actual info needed to really crack the ECU is closely guarded by tuners and it is up to amateurs like us to actually figure it out. So far, I am not aware of anyone that has.
The general idea that some people go with when trying to do a "cheap tune" with the stock chip is to run injectors that flow more in proportion to the amount of boost that they plan to make. 6 PSI means that you will flow ~41% more air, so you will need injectors that are 41% higher flow than the stock 210cc/min ones, so ~295cc/min. The thing is that you will run MEGA rich at idle and any time you are not making 6PSI, and it will be a really crappy way to drive. And you'll burn out your cat right quick, and burn through O2 sensors regularly. A less-bad way to go would be with an adjustable rising-rate fuel pressure regulator so that you can run higher fuel pressure under boost. That will end up being hard on your fuel system and there's no way you are going to get 40% more flow out of the stockers, though.
I know what you are aiming for as I used to think along the same lines when I wanted to do a "broke-assed college student turbo build" about a decade ago. You'll spend more money on the Ostrich, chasing issues and burning through fuel than you will on a dyno if you go the hacked-together route, so I recommend a proper dyno tune. The stock AFM can handle ~205bHP which my 2.1L M42 is built for, and it runs A-OK with the AFM all the way to redline. On 6PSI I doubt that you will have any need for a bigger AFM. I highly recommend putting the AFM before the turbo inlet so that it can accurately measure air input. It cannot account for density changes of pressurized air.
Another benefit of a dyno tune is that you can then read and compare the stock chip to the one you had custom made. That could probably help the M42 community to finally figure out which maps are the right ones (the stock chip has a bunch of different ones for the different global regions the car was sold in), and you'd have a great custom tune to get the most out of your turbo setup.
