Interlaced source cropping

[avl1]

Please help a confused newbie. I am trying to convert some interlaced VHS material to 352x480 interlaced NTSC XSVCD. So both my source and my output are interlaced. To save some bandwidth I would like to crop some black overscan and then center the image. In the process of vertical cropping I am loosing some scan lines, so to make the compliant interlaced MPEG2 I need to add the cropped lines at some stage to make their number 480. At what step should these lines be added? If I crop in TMPGEnc add then set the output frame size to 352x480 I am loosing the bandwidth again. Or should I set the output size to e.g. 340x470 and TV will add the missing lines?

[Shabubu]

You'd better do it in TMPGEnc, you won't lose bw as your adding black lines that compress really well, as opposed to the headnoise your cropping out which compresses badly.