Yup, a smack to a board will go straight to your transponder. That foam bumper is very soft. Much softer than the Trinity and less affective without a wide plastic bumper like the new RPM.
Why are you so hell bent to have it there anyway?
About the Losi rear hub carriers: Yes, it make the ballstud vertical and you will notice to clear the shocks you will have to run the car short and trim your ballcup a bit. The links will also be at an angle. I don't think the angle makes any difference to handling. I've run my car with the Losi front spindles and rear hub carriers and I like it a lot.