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I believe that the DblPAL (DoublePAL) monitor driver, normally found in Storage/Monitors, might do what you want. It outputs at around 28KHz, direct from the A1200's RGB port, and gives 640x512 non-interlaced 48Hz as standard. DblNTSC gives 640x400 up to 640x480 at 58Hz, and might be better if the DblPAL isn't quite "fast" enough.
("Normal" Amiga modes are 15.6KHz 50Hz PAL, and 15.72KHz 60Hz NTSC.)
Edit: others can advise on the best way to use a TFT monitor, my experience is with analog RGB CRT.
Further edit:
This makes me think that an Amiga RGB to VGA cable will allow you to simply plug in and go, using one of the above monitor drivers, however the native 1280x1024 resolution of the panel could mean less than optimal viewing due to the image having to be rescaled.
