I have used Magicmenu under 3.9 with a Falcon 1240 accelerator in the past with no issues.
Yes, with 4 MB fastmem you will be able to run 3.9, but dont pretend to use workbench with lots of colors and fancy backdrops, because that will eat you too much of your precious ram. Experiment a bit to get the best quality/performance ratio.
And remember to configure the workbench prefs tool to use other mem.
Good luck!
