i've got stage three crower cams and im getting the stage three head from slowboyracing that has the extreme port&polish done to it and im not gonna be running a turbo intil a month or two after the engines ben running so for the time that it dosnt have a turbo what size injectors should i use?

Well I am kinda lost, what are you going to run for a turbo, no need to buy injectors twice. So before I can answer what are your turbo plans?

im planning on getting the 20G turbo kit from hahn-racing

i would go with 660s or 760s maybe a 255lph pump and FPR to suite up that turbo.

But why a 20G??

isnt that the biggest turbo hahn racing makes for the 420a?

I didnt know you were working with a 420a platform I was assuming 4g63