Do your edits, add a reformat 4:3 effect to the sequense using a top filler.

After that, switch properties to SD and do a digital cut to tape.

Iam assuming you meant using the Pan and Scan effect under reformat. I set the source to 16:9 and target to 4:3 which gave me the correct size once the sequence changed to 4:3 SD. I will try your workflow tomorrow as suggested :)  - Very good that you found it, there is also a readycreated filter named 4:3 that doesn´t need any adjustments, MC gives you many ways to do things

Your initial question wasn´t about to mix Hdv and SD clips, you brought that up later in this thread, we will handle that to, the Sd clips will be added to the sequense once it has been switched to Sd

So, now for a test project, start with some captured hdv clips on an hdv sequense, nothing else

when you go to export, select the file in the bin, click FILE > Export > Options.  then select Export As Quick Time Movie  (Not QT Reference).  i've had problems on occasion with QT Ref files not ordering fields correctly, and using an actual QT Movie fixed that.  you will need to click the "Custom" button instead of the "Same as Source" to see the field-order options.  Click on "Format Options" & select the highest quality compressor you need to preserve your resolution  (under Video - Settings).  make sure to select Video Only if you're exporting the audio separately.

set your Width x Height & Color Levels & Field Order & Aspect Ratio (probably naitive dimensions).

you can change field order on clips in MC by creating a video mixdown of them (which orders fields according to the resolution selected) or you can export clips & re-import them with a different field order  (Click on "Options" in the file import pop up to change field order on import.

hope that helps.

shane