You could encode the video to 25fps and use DGPulldown to apply the relevant pulldown flags, and mux with the unchanged PAL audio. However I think you'd be better off converting the audio.

First you need to check if the PAL audio is a straight speed up, or a pitch-corrected version. Listen to a portion of the NTSC audio, then the PAL, and if the PAL sounds higher pitched then the conversion is a simple process.

(You should also check that the video ripped from the PAL DVD has the same number of frames as your IVTCed HD conversion.)

BeSweet is fine for the rate conversion, but the encoder BeSweet uses (ac3enc) is not as good as commercial software. Therefore, I'd output 6 channels from BeSweet and feed them into a commercial AC-3 encoder if you have access to one.