Fuselage:

The differences are mainly confined to the fuselage, which is Dominie length, (ie two feet shorter than the Srs 600, but with a smaller inbuilt step passenger door, 5 windows port and starboard, and a reduced size underside belly fairing ahead of the wing. (Dominies have navaids and radar housed here, and their much larger fairings extend right under the passenger door).

Working a Srs 400 from the Dominie kit would involve a narrowed passenger door, blocking the windows on each side nearest the engine, adding two front windows on the starboard side, and severe hacking away and reshaping the front of the wingroot/belly fairing.

All of which would involve more work than the simple 2 feet (1/3 inch in 1/72) fuselage chop and front window blocking and 'skullcap' addition to the Matchbox fuselage. So, after carefully marking the surplus area immediately behind the passenger door using masking tape, work started with the razor saw. No turning back now!

Tail:

The top tail section above the T Tail is shorter (by 13 inches) than the Srs 600, and has a small root / intake, as per the Dominie, so the tails were swapped.

Main wing:

The Dominie kit does show its age, with gimmicky moving control surfaces and raised panel lines, but looking at a few of the photos in the Bill Gunston book, the control surfaces do seem fairly prominent in comparison to the trench lined and rather plain looking Matchbox wings. The Airfix wing simply needed some trimming and filling to fit the Matchbox fuselage. One of the two Mercurius photos in the SAAF book shows spoilers slightly extended, so I decided to add this detail to the model, by hollowing out the interior space then adding strips of plasticard. Plasticard was also used for the outer lower wing fences, which are not featured in either kit.

Lower fin / Main wheels:

Different from both kits, on the Srs 400 this is a simple triangular section. I simply trimmed the excess leading edge from the Matchbox fuselage. Mainwheel doors and undercarriage: Doors covering the wheels were a new feature of the Srs 400, so the Matchbox parts were used. The Airfix legs are more sturdy, but the Matchbox wheels look better, so this combination was used.