I find no fault with the syntax of:
“What use of the noun do the heavy type endings suggest?”
Heavy type is a transparent synonym for bold type, used by the page layout people I used to work with.
I had not the slightest difficulty understanding the sentence. I live in a port city where ESL (Koine English) is the language spoken on the street.
You made me doubt my memory, so I did a search for “heavy type” on the English Wikipedia, the font of all knowledge 
. Nothing turned up at all, but there was a result for “bold type.” I also searched for “heavy type” in Google and got nothing relevant for the first two pages. There were results, however, for “heavy typeface” and “heavy font.” Perhaps “heavy type” is not a very common term.
Also, during my education, I was taught that it was mandatory to put a hyphen when the grouping of a compound modifier will not be clear to the reader. I personally would never write “heavy type ending” or even “bold type typing,” but always “heavy-type ending” or "bold-type ending’’ to avoid precisely the confusion I initially had, thinking about “heavy syllables” and similar terms. Moreover, in my English, “bold-type endings” is just not an idiomatic phrase. I would always rephrase it as “endings in bold type” or something similar.
Postscript: Back in the 80s I shared an office with native speakers of Mandarin and Cantonese who spoke to each other in English. My workload wasn’t very demanding so occasionally I would help the engineers clean up their English in technical publications. The guy from Hong Kong needed no assistance. I recall an engineer from Korea who needed help with syntax, particularly the use of the English direct article.
Years ago I was introduce to a professional translator from a tribal culture in Central Asia (goatherders who live in tents). She spoke perfect English, zero accent. Much more intelligible than a native of rural Alabama who has lived on the west coast for 40 years.
Years ago, I really struggled using bilingual Collins dictionaries, I had difficulty understanding many of the entries. Only after some time did I realize that the issue was that the definitions were written with British English in mind. For instance, don’t “table” matters in England and the US and expect the same result, because the expression has opposite meanings depending on where you are.
Back to Mandy’s journey, I think that Jeidsath’s suggestions are good, but do you think Mandy is likely to get anywhere useful using this book? I am not familiar with it, but seeing Latin endings in a book teaching Greek gives me pause when considering the average learner nowadays.