250mm for the inner barrel right up to the end of the outer.
GM 3.5 nozzle, but take the seal off the back of the stock nozzle (GM rear seal isn't compatible with DE BCG) for being able to fit an NPAS - NPAS doesn't fit in stock DE nozzle.
Jaeger or FEDA for NPAS - former is easier to get hold of in the UK, latter has some QC issues as of late.
Bavtac/Jaeger nubs aren't compatible with DE hop arm, unless you want to overhop .48's with no hop applied ofc.
MR hop rubbers contact patch get eaten by the nozzle on both stock and GM, so something flamingo or similar (which is a bugger as flamingo are flimsy).
Did it have a black or silver BCG? If its black (V2), the mags are good, if its silver (V1) you'll want to get something else.