there is no need to get exotic with a pressure regulator or the injectors. the press. reg. works by increasing pressure when vacuum is reduced, ie: wide open throttle or under boost conditions. the early L28ET engines used the same pressure regulators as the N/A version did, and never had any problems. unless it is leaking or won't hold pressure, there isn't any reason to change it.
for injectors, use the figure of 1.4-1.6 to multiply engine displacement, in your case 2.1-2.4 l disp. as a baseline figure for fuel requirement, this will put you very close to the necessary increase in fuel. there are a good number of stock injectors that you should be able to aquire from your local wreckers for a reasonable price without needing to spend a ton of money. think of CA20, FJ20, and KA24. the L serier 6 cyl. ones will work but might run a bit lean.
referencing another post you made concerning MAP sensors, IF you got the Saab 900 turbo (93-98) there, they also use a Delco system and are set up for boost, if not let me know I can get you one.