GSUB table for a font

I'm making an Indic font and some letter combinations have to be replaced by a single glyph and so on. I've never designed a font requiring substitutions. I studied Kalinga font supplied with MS Windows and applied what I learned but the conjuncts aren't working: even though FontForge shows that they would. Been at it for 2 days, even tried MS Volt but couldn't figure out anything. Any help will be appreciated. Attachment 106628

I only installed FF once, ran it once just to have a look at it for another person. So I really have no idea and recommend posting on their forum if there is one. Otherwise they are still using a mailing list and you would need to subscribe to use it.

It's been a seemingly long time since I used VOLT and I doubt I would be of any assistance. Sorry.

Mike