Here is my approach:
with the front bumper; you can cut the lower part from you old bumper, bellow the red line in the pic
Then this part needs to be cut away
then the lower part of the veilside bumper needs to be made with styrene and putty (A) .
The B part needs to be cutted and moved back, then fill with putty
(it's hard to explain)
Thats the way i should have done it i guess.