Mango,
Yes, I think you could mount the 540's. I looked at some on display at one of the truck shops and they looked real good. I think they measure at 5 1/8", so they should fit.
Do you know if the opening is 5 1/2", or tapered smaller towards the rear. I pulled one out a couple of weeks back, but re-installed it before I measured.
I was thinking of doing the same install as you, with the 540's. I think you can mount them thru the plastic to bumper.
