Dear Colleagues

A question about XeLaTeX and the font Devanagari MT.

In order to produce Sanskrit editions in devanāgarī script with several layers of apparatus, I use XeLaTeX.

My font of choice is Devanagari MT, but running XeLaTeX on an input file that calls this font does not always produce good ligatures.  It sometimes uses a virāma under the first consonant instead of joining it with the subsequent one.  

I have found, with help from Dominic Goodall, the XeTeXglyph numbers for almost all of the problematic cases.  For example a correct devanāgarī ddva is produced by typing \XeTeXglyph286.  But these are the remaining problematic cases I have:

dba
ṅna
ṅga
ṅka

Would anyone happen to know what the XeTeXglyph numbers are for these?  Or know how I could find out?

Yours
Alex