Found this info in another Impco catalogue (Aren't they great?
)
The catalogue lists for a lot of different manufactures and models the required mixer to use for CNG/LPG fuels.
It also lists the different GMC V6's.
What I found more interesting was that different manufacturers used the GMC V6's (I read about this on Jolly's site)
Both Hyster and Yale used these engines. Both are the C (heavy duty) type according to the catalogue.
Hyster forklifts:
Models H-150E, H-165E, H-180E, H-200E, H-225E, H-250E, H-300E, M-200H and the M-300H. These all used GMC 305C V6's. Some were also equipped with other diesel engines.
Yale forklift: Model G-3 also used the GMC 305C.
Here's a video of a Hyster H-165E with the 305. I recognized the sound immediately.
https://www.youtube.com/watch?v=-DBFx8T4Kys
Could be interesting for parts etc. I hope you find it useful.