Hi, just saw this topic and thought I would comment, having had problems with my 13x855 mm belt before.
I use the 855 on my M30B35 and it is still very tight. The only trick I found to get it on is to use the starter motor.
The tensioner doesn't require much pulling, because it's already quite tight.
To get the belt off I have no choice but to cut it. If anyone knows how to get it off it would be great!
I made a video on this topic on my youtube channel. I'm sure it's not the proper technique to get the belt on, but it's the best I could find. Maybe it helps others.
https://youtu.be/qaTemeF7lOI