1972-78 RN2x axles are 1370mm drum face to drum face while the RA23/28 is 1374mm. So its actually shorter / the same and not a problem for teh RTA most of the time as you are using a complete unshortened axle.
The next model Hilux RN/LN 30 series is 1410mm, so you need to shorten this one to fit it. This can cost anywhere from $500 to $1000, so shop around.
Mitch.