The sections that your are interested in are those that define and outline the PLAYING CONFIGURATION as opposed to the STARTING CONFIGURATION. Also read several times the section 4-Robot, R07.
It is my understanding that your configuration would be legal. Team Update #1 has been issued and the dimension has been clarified as ”84” (213.4cm) diameter vertical right cylindrical volume.
The bumpers are part of the robot so as to minimize damage from robot to robot physical contact.
BUMPERS have several advantages, such as reducing damage to ROBOTS when they contact other ROBOTS or ARENA elements, and being excluded from the calculation of ROBOT weight and volume constraints specified in Rule <R11>. The BUMPER location and design have been specified so that ROBOTS will make BUMPER-to-BUMPER contact during most collisions.
Please remember that all other sections of the rules apply to your design as well. when in doubt, please form your question on the Q&A when it opens.
As for losing the protection of your front bumper - no whining if your forklift gets mangled in every round! - perhaps driving with the “fork” a foot or more off the ground would allow bumper-to-bumper collisions? Just high enough so it doesn’t impale other robots.
Ummm… maybe forks IN the bumper zone would be better, 1 foot off the ground sounds like it will be right around all of the crucial components on some 'bots. At least if it hits the bumpers the plywood would probably stop it if the fabric& noodles don’t. I would say ~4 inches above the ground sounds better.