S class (89) rear bumper construction question (fitting reversing sensors)

Got a question about how the bumper is constructed. Read on...
I want to fit some reversing/parking sensors into the bumper. Got myself a nice setup off the Ebay.
I've had a look up and inside the bumper from underneath (with the bumper still on), and can see a heavy gauge metal reinforcement in there, with the chrome strip fastened along and above this with screws. The chrome strip makes judging gaps difficult because of the way it fastens. What I want to know is:- is there is a gap between the metal reinforcement and the inside face of the bumper (plastic portion). If there is, I may be able to just cut holes through the plastic, and run the wires out and over the reinforcer. If there is no gap, have I got to drill through the hole thing? That will be much harder as would be expected. Any guidance on this construction would be helpful before I start something I may regret.
Cheers... Rob.
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Might help if you can tell us if your S-Class is North American version or not. The bumpers are bigger and 'meatier' on North American versions.
Rob. Smith wrote:

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oops
sorry about that. I forgot that USA versions have beefier bumpers. Its a UK model. Cheers... Rob.

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