1970 Camaro BIG Problems +++ please help +++

[JJEH]

Okay, I just got a call.

All the rusty $hit is gone, the workshop fixed all.
Suposedly to the "agents" (Germann Company) expense...

Now the only matter is the engine.

My brother said he wants the ZZ3 engine but it's just a 305ci in.

The seller told the "agent" it's a 350ci in with the ZZ3 Kit.
The Kit brings more ci and more HP the seller said.

My question is, how can I absolutly identify the ZZ3 engine?
And what is the Kit for?
How can I tell the different between kit and engine?

Thanks Guys for your help!!!

BTW: There was no contract between seller and "agent..."