Correct, NA engine with 24# injectors and a custom tune. Really, the custom tune part is where it is all at.
I am running a TRE Performance 255LPH pump. Again, I only switched to it because it is $70, rather than $150-300 for a stock Bosch one. Lots of guys have run turbo setups with the stock pump. This is the one I went with though. Unless yours is dying, I don't see any benefit from a higher capacity one unless you are going to run over 15PSI of boost.
http://treperformance.com/i-6323866-bmw-318-255-lph-fuel-pump-1990-1999.htmlIt is not a 100% straight-forward swap as you do need to Dremel the bracket a little. See this thread in r3v, and just ignore the parts about the 2nd pump since we only have one.
http://www.r3vlimited.com/board/showthread.php?p=1968663A wide-band O2 sensor is really only necessary if you plan to do your own tuning. Otherwise, dyno shops stuff one up the tailpipe and tune with that.
A number of M20 guys have done turbo setups over the years they have an adjustable FPR in there to "fudge" things rather than tune the ECU. It works, but not as well as a proper tune. You'll end up getting lousy mileage and have poor control over the air/fuel mixture. As far as adapting an adjustable one, someone else will need to chime in as I am not sure how they mate to the rail. It seems unlikely that they will fit where the small stock one is.
Just FYI the stock one is a rising-rate regulator, meaning that it will keep the fuel pressure at 43PSI regardless of the pump pushing it or the manifold pressure. That is much more critical than messing with the system pressure. A much better bet for you is to determine how much more air you will be flowing and then put in injectors of a larger size according to that ratio. Raising the fuel pressure puts more stress on the rest of the system needlessly and is basically the "wrong" way to go about getting more fuel in.
For example, if you are going to run 7PSI...
14.7PSI is atmospheric pressure, and the manifold pressure is about this when at full throttle. With 7PSI of boost, you will have 21.7PSI in the manifold, which is 47.6% higher, and roughly means 47.6% more air flowing into the engine. The stock injectors are 19# units, and 47.6% more than 19 is 28#. So, at full throttle and full boost, stuffing in 28# injectors should get your AFR right where it needs to be with the stock ECU, in theory anyway. In reality, you will run rich as hell all the rest of the time, fouling plugs, ruining your catalytic converter, fouling the O2 sensor and probably having a check engine light. Your idle will also be crap, and it will generally run poorly.
I don't mean to rain on your parade or lecture you, but your #1 priority should be selecting a shop with a dyno to make you a custom chip. Give them your intended boost level and the size of the stock injectors and they can probably recommend new injectors. From there, it's just a matter of making everything fit and then getting the car to the shop for tuning. Thereafter, it will run great, idle great and be a hell of a lot faster.
Trust me, I have been where you are at a couple of times in the 12 years that I have owned and modded M42's. Dyno tuning is $$$, probably almost as much as the turbo parts, and it always seems tempting to try to find cheap ways around it. In the end though, you will end up with a turbo car that doesn't run nearly as well as it could without taking care of the ECU. Old carbureted cars with distributors were "easier" to do this with since there was really very little you could do to optimize the entire map, and everyone just generally accepted the fact that "more power = crappy idle & driveability." With a more modern car with an M42, the fully electronic injection & ignition system means that you can go worlds beyond the old ones if you spend the time and money on a tune, and get a car that runs great around town and also hauls ass when you want it to!