I bought and assembled 60052 Cargo Train. The holes on the top of the engine bother me so I wanted to cover them up. I ended up making a bunch other modifications along the way:
Added Power Function LED ditch lights
Changed style of radiator grills
Added air intake grills
Added dynamic brake grills
Moved fan #1 forward for dynamic brakes
Moved fans #2 and #3 further back
Added exhaust port
Covered up unnecessary openings in the roof
Changed to smaller sized horns
Changed style of fuel tank
Switched doors around so they are no longer suicide doors
Added dual transclear stud lights to back
Changed bley brack in front roof to black
I guess it looks a bit like an EMD GP38 now. Please excuse my messy building table.
60052 MOD by dr_spock_888, on Flickr