Crud, I hadn't thought of that . . . these are NTSC speed. I suppose you could decode these into their separate channels and speed them up, then re-encode to AC3 again, but that would be more of a quality loss . . . or I could apply the shift to PAL speed myself, going from the original PCM files directly, so there will only be one lossy encoding stage.

Edit: Adywan posted before me--I didn't realise you could do that with BeSweet. Does that involve re-encoding, or is it a lossless process? If so, that would be the easiest and best way to go.