Use SolidWorks to Combine Two 3D Models of USPS Mailboxes into One

We have two 3D models of USPS Mailboxes and I need you to merge them into one. Background info: The US Postal Service deploys two kinds of mailboxes in our sidewalks: • Relay Mailbox: Used as storage to relief the back of the patriotic, hard working, underpaid mail carriers (*). It has a door, not a slot. It is bigger than the one below. Their color is an ugly green/brownish. • Street Collection Mailbox: Used by the general public to deposit, the mail carrier to collect. It has a slot and a door. Their color is a very American, attractive blue and red that can be seen from far away. Source files are here: [login to view URL] Reference files here: [login to view URL] Here's my problem: • The Relay Mailbox is completely ready. It has perfect level of detail, can be uploaded to Sketchfab. • The Street Collection Mailbox that I have was meant to be suitable for manufacturing or rigging. It has levers, hinges, screws, etc. Therefore, its file size is unmanageable. I need a new one, plus decals and a very nice, professional look. I would like to upload it to Sketchfab, so I can impress my potential sponsor. You may start with either one. Probably the best approach is to remove the internal parts, hinges, etc. (simplify, simplify, but not too much) from the Street Collection Mailbox provided. You must be an expert using SolidWorks for similar work. A degree in Mechanical Engineering is a plus. The most I can afford for this project is $120 BUT there may be additional bonus. (*) We don't want them to go postal on us.