I was following that guy's build some years ago with interest (as the MB5 is one of my absolute favorite aircraft), he started off building the fuselage 1:1, but then I saw he was going to use a Mustang wing and got disillusioned with it. An MB5 is about 1 1/2 times bigger than any P-51 and the wing he used just looks really odd on his MB5.
When building my model of the MB5 I found that the wing is very close in size to a Grumman Hellcat wing, that is from the wing fold joint to the wingtip though. Even the flaps and ailerons are almost bang on for size and placement. Tailwheel assembly is very similar to the Grumman tailwheel design and the main gear are more like P-47 legs (they retract behind the wing spar too just like the MB5) but without the mechanical leg length shortening device. Wheels are Tempest size, or Sea Fury.