New Build/reno GMG940

[Macarrra]

Good afternoon to all

Thanks first of all for allowing me to be part of the forum, I hope it'll be helpful to learn from your group wisdom.

So last week I bought a 1969 GMC 940 2 ton dump truck.

She is a little tired and not working perfectly, but I have decided to try my best to bring her back to a great condition. While I have done some restorations in the past, it was all much smaller cars, so this is a new beast for me.

To my knowledge the GMC940 is a Canadian badge for the Chev C50 (or maybe C60?!?).

The engine needs some love, and the brakes dont work very well at all, so im starting by trying to learn exactly what's under the hood, so I can then learn how to research each aspect.

So my first questions, if you have the time to reply, are:
-exactly WHICH engine do I have under the hood?
-can you confirm if this is a vacuum brake system?

To my knowledge, its a V8 350, however upon some research it seems that there were three different models (307, 350, 396 cu in).

Can you tell from the pics below which one mine is? Otherwise any suggestions on where I can look further for identifying features.

The brake resevoir may not be the original one (it seems more modern that other parts under the hood). I'm told that this model should be a Vacuum brake system, but wonder if someone can confirm that. When I go to brake theres a loud hissing noise and the brake pedal eventually kicks back (and the truck really doesn't some to a standstill very quickly!).

Many thanks in advance for your time, I'm sorry for the lack of knowledge...but its never too early to learn new things, right?!?

I will occasionally post build updates if people are interested, perhaps people arent though

Thanks to all from British Columbia (CAN)