Most FPRs have a clip that pulls out and then you work them up and out of the housing GENTLY or you'll knacker it.
With 440cc injectors you shouldn't need a 4bar reg to start. Leave the 3-3.5 one in there and map the period they stay open appropriately.
Go to 4bar if you're approaching the top end of the injector duty cycle - it'll get you some more juice through them.
For thin intercoolers check out Sprinter vans - big and thin. Alternatively you could have a look at Merc C-Class Kompressors - their intercoolers are in one side, out the other, with nice swept bends on the unit, they're deep and compact and will probably fit in the lower opening in the front bumper. I have one here you can try on Sunday Saturday, if you want - I'll bring it to the meet.