Ahem font missing x-height record

There are files that attempt to use ex unit, but the x-height value is
actually missing in the Ahem font which is used for testing: according
to ttfdump (Microsoft's or FreeType's) OS/2 table size is 78, and the
offset to the x-height value is 86. Is it possible to use the font which
actually has x-height value written in it, so that there is no
guesswork?

 

Peter