Hey Shaun,
I see no one has responded so i'll give it a try. I have an HBW100 on my 82 5432. There are 3 ratios in that model: 1.48, 1.79, 2.72. I have the 1.79:1. When I put on a Gori prop, i wanted to be sure so I marked the output shaft and turned the engine with vicegrips 1 3/4 turns. The output shaft went around 1 rev so that was close enough to verify the ratio.
(use the decomp lever to turn the engine and eliminate the very unlikely chance of a cyl firing)
The HBW 150 ratios are: 1.56, 1.88, 2.63. Very close to the 100 model
If you use this method to check ratios be sure you are in forward as reverse is a different ratio. 1.86 for all the 100s and 1.95 for all the 150s.
I also have the dimensions of both trannys so if you could measure the width it would be simple to determine the model.
Hope this helps....