bongweeyap : nice nick btw, and thanx for the question. as i never mod an L2 dat extensively, again, what i may say will be base on theories and logic.
economically, u shud make an adaptor for ur new turbine to sit on. i know millennium can provide dis for less den a hundred ringgit, or at least d price tag is around there, the last time i heard it. a banana is usually better, but an adaptor is sufficient enuff. just bare wit its restrictions until u can get a banana fitted in. as i said, metal head gasket adds cylinder wall height hence messes up ur engine timings. i dont say it shudnt / cant be fitted in but do the calculationss rite, timings shud be done according to additional height. its not as simple as putting the metal gasket in, and just let it be. yes, many had done dis and say, "okie maa, mana ade problem!!" but use ur logic, and consider wether what i said r true. u miss on ignition firing, problem(s) may occur out of it. if nuthing happens, then its ur luck, but precission and luck seldomly work together. being precise, u r actually avoiding problems.
regarding on ur injectors, u have to know what is the limit of ur set. sum can be maxxed out, sum cant. or at least what is the max can any typical L2 injectors can handle, u get me? u wont know all this witout hooking ur engine on a proper tuning aparratus, u cant say ur engine is slightly lean or rich just by looking at exhaust puff. a set of wide band is needed in order to see dis, and most importantly a good tuner to set it rite. actually u can play boost as high as what ur fueling system can cope wit, AND what ur block can handle.
regarding the fueling and ignition system, u cant fully utilise dat big turbine witout proper tuning. witout proper tuning, i think instead of using a bigger turbine, its better to make full use of ur std turbine, as i experienced it. the std turbine can be pushed to an extend, it surprised me. wit the experiments iam doing on my current engine, i can get 1 bar of boost as soon as i plant my foot down even on lower revv. iam not saying my engine doesnt lagg off, but i can minimize it by throttle control and sum mods on the turbine and actuator. i once asked my lil brother to mod sumthing on my actuator, and when he drove my car, he accidentally boost to 0.96bar at a mere +-3k rpm, he told me it was lower den 3k rpm, but lets just take it at 3k rpm. dat shows how the std turbine can response to throttle input, FAST!! dat mod costed me the turbine. well, costed me +-RM300 for a new turbine, but was well worth it because i now know what to do in order to get it rite. once the farked up turbine was opened up, i can find anything wrong wit it, but it cudnt boost. dat turbine is now in rebuild process wit sum kacuk mod. i hope i get it perfect dis time
oh, like bro beyond said, use a larger fuel pump capacity. dis wont affect ur FC as u can still tune the fuel pressure once u get an EFN AFR (iklan, hoho.. EFN, belanja minum k), bigger capacity fuel pump ensures ur engine gets the fuel it needs everytime.