The lock ring is ~5" across, so a hole only 7" front-to-back is more than enough to work through.
Before attempting to disconnect the fuel lines, read this caption:
Older fuel lines are much easier to remove.
Once they're off, and the plate is clean, use a non-sparking (brass) drift & hammer to turn the lock ring CCW. If it's stuck, the only acceptable lubricant is CLEAN MOTOR OIL. No penetrating oil; no silicone lube; no grease; no WD40.