I'm looking to work with 4:3 anamorphic rushes 2048 1536 within mc, un-squeezed, which is no problem, but am looking for a way to display squeezed and cropped output, ie 2:1 letterbox within a 16:9 frame on a client monitor.
I'm trying to figure this out on my end but am testing with source material that isn't similar to yours at all and am just having to pretend that it is, so sorry if this is incorrect.
I think I know what you should do to have the footage display as you want, however it would display that way on BOTH the client monitor and your computer monitors. Don't know if you specifically needed to look at the material unsqueezed or if you just didn't mind it.
If you want this to apply to all the clips in your project, you can load them all up in to the media tool, drag them to a bin and take the below steps, but I'd suggest maybe doing it small scale first, you could do it with the reference clips of a sequence for example.
Admittedly I don't have any anamorphic footage to test with, but I took some 16:9 stuff and re-encoded to those dimensions so it looked squashed and then tested this in a 2048x1536 avid project and it works on the computer monitors. I also don't have a client monitor to test with now either, however my understanding is it should output to a 16:9 screen with letterboxing slightly thinner than what you see on your own source and program windows. The nice thing about this is it's all reversible, if you don't want to remember to go through every bin and remove the frame flex changes you made, you can just do it at the picture lock stage to all the clips in the sequence. You can just select all the reference clips in lock picture bin, go to the frame flex settings again, click the little two lines icon next the 'image size' drop down list and click it to reset the image settings back to what they were, and then click on the 'reset' button in the bordered box of settings under 'FrameFlex' and then 'apply to all'.
Sorry I can't be more definitive, but I'm not currently setup to properly test this. If this doesn't output to the client monitor the way you want after that I would suggest ditching all the frameflex changes and looking at the I/O card's own configuration software which depending on the card may allow you to do things like set the display aspect ratio and image processing settings to accommodate it.