1440x1080 with 1.333 Pixel Aspect Ratio means that it gets stretched to 1920x1080 during playback (it's what is also called an AR flag).
So even if it looks 4:3, it's fine, because 1440x1080 is a 4:3 resolution, just when importing the footage in premiere, right click it and tell premiere to assume it has a 1.333 par flag, and it'll get it right.
You can of course stretch it to 1920x1080 yourself, however you'll just inflate filesize quite a bit for no actual detail gain, so that's your call.
Mpeg files should be fine in premiere, however, what with lossy editing and all, I'd say that, if they are mpeg-2, you should just index them with dgindex and treat them as if they were a DVD, so to speak.
If by mpeg you actually meant mpeg-4 AVC (which would make sense too), then you could try remuxing them to mkv and using ffvideosource on that or, if you have hardware and/or money to spend, try DGDecNV or DGAVCDecDi.
After that you just make the avs as usual and edit like you're used to for AMVs.