FX-39 is now hard to find in the US, where the OP lives. See the APUG non-staining developers section for the FX-37 formula, posted by Gerald Koch, which Crawley says is the published formula closest to FX-39. FX-37 was formulated for T-grain type films, but is said to work well for slower traditional films or higher speed traditional films at enlargement factors less than 12.
I like Rodinal 1:100 and reduced agitation with slower traditional films, and have had good results with Gainer's suggested addition of sodium ascorbate for this application.
Lee