Hello from a newbie and questions

Hello everyone I'm new to motor biking, this forum, and mechanics in general. The other day I was surfing ebay for a bike and happened upon a BGF z80 kit ad. Instantly was like "hmm I always wanted one of those as a kid" so without researching (normally do) bought it. Anyways on to a few questions.

I plan to attach it to a mongoose mtn bike, the bottom bar of the frame is square, really wide, and thick. Couldn't find any info on anyone even attaching a motor to a mongoose... Wont mind drilling if need be.

Any advise would be appreciated for both mounting and general care/assembly/things not to forget ect.

Edit: Lower bar is 2"x1.5" depending where measured.

Thanks for all your reply's everyone! I'll get to reading and post a pic soon.
Back to properly reply to all of you.

@Hoze - Thanks man I managed to find a complete build of a bgf engine on youtube.

@AL - Thanks for the pdf and photos sure will come in handy.

@Slowbalt - Added pics

@ 2door - Thanks for the reading material.

pics posted