Is/was there ever a 340 Magnum

The "340 MAGNUM" hood emblems were part #3573632 and used only on the 1971-'73 Charger and '71 Super Bee. There are similar Charger-specific 383, 400, and 440 Magnum emblems from 1971-'74. In 1974, the 360 Charger's hood emblems said only "MAGNUM" with no displacement callout while 400 and 440 cars still spoke of their cubes. Plymouth B-bodies exclusively used displacement decals in the same years, with 1973-'74 440 Road Runners having a small metal "GTX" below the 440 decal on the hood.

The Challenger R/T's "383 MAGNUM" (1970-'71) and "440 MAGNUM" ('70 only) emblems are considerably smaller than the '71-up Charger parts as well as the Challenger's Hemi and Six Pack emblems. Early 1970 340 Challengers (A66) had "340 FOUR BARREL" hood decals, while later-production '70 and all 1971-'73 340 Challengers used similar-looking metal emblems. 1974 Challengers used a "360 FOUR BARREL" emblem what-fer there warn't no 340 no mo'.

Some confusion may have come from the fact that early Challengers were available with different versions of a 383 including the HP Magnum version. I'm sure 331IMP's friend has a 340 FOUR BARREL emblem if it's original.
Non-R/T 1970-'71 Challengers had a "383 FOUR BARREL" emblem on the fender rather than the hood.

Air-cleaner paraphernalia, be it a pie tin or decal, said "340 FOUR BARREL" on everything except Six Pack/Barrel engines, what with the obvious difference in venturi population 'n' stuff.