i found this in another web site discussion, it seems accurate to me. i have a 71 Charger 500 that i put a 73 bulge hood on soley based on the funds availble at the time.
1971 Charger hoods, three used
3482 018 Flat hood used on most models
3482 535 "Power Bulge" hood used on R/T and SuperBee models, w/inserts * (one year only)
3482 471 "Power Bulge" hood w/fresh air induction, "Ram Charger" hood * (R/T and SuperBee only, standard w/Hemi)
* - Power Bulge hoods with continuous vents or with a center gap can be considered correct.
1972 Charger hoods, three used
3482 018 Flat hood used on most models
3482 471 "Power Bulge" hood w/fresh air induction, only avail. w/Rallye pkg. A57 *#
3611 212 Used on WH23, "Sport Hood"
* - Power Bulge hoods with continuous vents or with a center gap can be considered correct.
# - Replacement Power Bulge Ram Charger hoods have been found with 73 style vents and the 3482471 part number stamped.
1973 Charger hoods, two used
3684 033 Flat hood used on most models
3684 031 "Sport Hood" (power bulge) *
* - The vents were reduced in length and had a larger center gap in 73.
1974 Charger hoods, two used
3752 174 Flat hood used on most models
3752 473 "Sport Hood" (power bulge) *
* - In 74, the hood vents were eliminated completely.
I believe all the power bulge hoods in 1971 had engine call-outs on both port and starboard and only appeared on the R/T and SuperBee.
The gap between the vents (1971 models) has been an on going topic of 'discussion'. As far as I know, there are only two variations. One, a continuous row of vent opening across the back of the hood panel and two, two sets of vent opening separated by a 'gap' of unvented hood panel. There have been assertions that the width of this 'gap' also varies.
The contention is primarily regarding when hoods with the 'continuous' vents were replaced with hoods with the 'gap' or vice vesa. My personal opinion is that it is more likely due to which plant manufactured the panel.