I think your floor pans are different enough you'd have some fone making it fit.
However, there wasn't an OEM rollbar for '73 -- that came in '74 (model years, anyway.) Your potential donor is likely aftermarket, which might well fit better into yours.
The OE rollbar has four feet which bolt flat to the floor, two right behind the seats and two farther back, and two big tabs (~2" square) which bolt into the bedsides just behind the seats. I can prolly provide pictures to assist in ID'ing if you need.
Aftermarket ones usually bolt to the floor on the front feet and to the wheel wells (at an angle) on the back.
-- A