Good questions to consult the rulebook:
http://www.casc.on.ca/roadracing_rules
Bumpers:
Appendix N, 9.12 Bumpers may be removed, except when they are an integral part of the coachwork, in which case they may be replaced with replicas of a different material. If the bumper is removed, all projecting hardware, brackets and fixtures shall be removed.
Arm restraints - not listed in the rulebook (hmm, maybe something should be said), but I believe the practice used in the region is that they are required if there is no window net on the drivers door, but I did not think it was needed if not running the hard top.
Rear window - also not explicit, but I believe you can run without a rear window.