On original cars, was there just one key that operated all the locks on a car ?
In my case ,1970 Cuda.

No, all Mopars that I know of ( from the early 1950s up to the mid 1980s at least) have always had two keys,(triangle or not round) ignition and door locks with the other round head one for the trunk only.

Glove box?

Maybe the same as the trunk, maybe not

1 key for doors & ignition
1 different key for trunk & glovebox

All Mopars, back to our '57 as I remember, maybe further back than that.

Fun fact: ignition key from our '57 also worked in a neighbor's '66 Coronet; both cars were purchased new from separate dealers, obviously years apart.
I discovered that by accident as a kid just fooling around...
Later learned that - duh - there are only so many combinations available...

Yup. 70 RR...same key for doors ignition... 1 for trunk...1 for glove box.. no idea if any were changed at some point in life,,,,,

Another fun fact; the Police Package cars were single keyed, at least in 70's and through the '89 Diplomat. The one Pentastar Key worked doors, trunk, glove box, and ignition. On the Window Sticker for '89 Diplomat it's code GXB - Key/Single......$18.00

It was pretty much a matter of having the truck lock tumblers changed to match the door locks. The glove box door was a bit harder to do.
I used to have a big key ring of old Mopar keys. Often times keys for one car would work in a different car. That was the reason they changed the groves on the keys every so often. Gene

Actually, there are a lot of combinations. I just don’t have phone to calculate it right now. It’s calculated 5x5x5x5x5=? As a locksmith I can tell you that some keys will work when in other cars when the pins or tumbler are worn and just close to the same as another. I just changed my 05 dodge for the second time because because the lock was so worn, almost any key would work. It’s an in town service truck that gets lots of key removal.

I actually sell a single key system for the 70/72 Cuda and 70/71 A/B-body.
The trunk operates off the same key as the door/ignition.

Back in the day my 69 dart and 70 Cuda had exactly the same trunk key..I didn't notice for several years.

If you desired & had some extra locks to play with you could match tumblers/spacers to where (1) key would fit everything. move the tabs on the chrome rectangular cover just enough to the cover comes off (they are brittle) so you can access the innards. & if extras are in short supply you dont even have to match all 5 holes & no one really picks car locks anymore (except in the movies). & it wouldn't hurt to use graphite lube sparingly when you are all back together.

Way back when, mom & dad bought a new 76 Valiant 4dr . . . I was in High school, and a buddy had a 71 4dr Fury . . . he tried his key in the valiant - worked perfectly !!! . . . . fast forward to like 98 and I had a Dynasty company car . . . key from it fit in my buddies 93 2500 !!! . . . Crazy that people you KNOW would have same key for different vehicle !! . . .

The 72 Barracuda we have was purchased new by me. It has one key for the ignition and doors and a second key for the trunk.