As Roobarb mentioned in the Duxford thread about PT462 and the use of the short span ailerons, it would seem that Dick Melton favored incorporating modifications that he felt improved, and were best for the Spitfires he was restoring, based on his experiences with them.

(Again, as Roobarb said, and attempt to try and get the very best out of a restored airframe it would seem, from both a build standard and the flying qualities).

Looking at the various CAA Airworthiness Approval Notes (AAN) for the Charles Church Spitfires, he seemed would include modifications that went beyond that particular Mark being restored, so a MKIX for instance would have modifications that were incorporated up to the PR.XIX, or later.

Here is an excerpt from the original AAN for MK.IX PL344/G-IXCC: –

Restoration is LF Marque IX standard using modern materials and incorporating numerous
modifications not previously associated with this marque of aircraft, but incorporated in subsequent
production marques as improvement modifications. All original radio, armament, oxygen, camera
and electrical equipment has been deleted rendering modifications related to this equipment not applicable.

Below is a another section of the AAN which lists the types of modifications incorporated into the rebuild of PL344: –

Mr Melton has raised modification Spitfire DM 043 to define the build standard of Spitfire GIXCC,
to list its equipment and provide a record of the modifications incorporated at restoration.

Each of the listed modifications have been evaluated for its effect on the airworthiness of the
aeroplane.

Modifications have been introduced in five categories as follows:-

a) To introduce essential modifications and inspections as promulgated by MoD and the RAF
in AP 1565A and E Vol II Part 1, AP 1565 J & L Vol II Part 1 and AP 1565 W Vol II and
various STI’s. (Schedule I and II of DM 043).

b) To selectively introduce modifications published in AP 1565 W Vol 2 Part 1 Leaflet Z26
for later marques F14 to F24. (Schedule III of DM 043).

c) To incorporate modifications published by the Battle of Britain Flight. (Schedule VII of
DM 043).

d) To introduce product improvement modifications generated by Mr R E Melton. (Schedule
VI of DM 043).

e) The following Dick Melton Aviation Mods have been introduced DM
032/034/035/038/039/040/041/042/043.

In many cases original Supermarine drawings have been used, but a full set has not necessarily
been available and drawings have been introduced by Mr Melton as required.

I’m sure Roobarb will be able to give more info especially regarding PT462 (and PL344!), but as you can see, Dick Melton not only incorporated later modifications from later marks he deemed appropriate or necessary, but also his own which he felt were improvements (a modern and simplified electrical system with an alternator for example).

For those interested, here is the link to the original AAN for PL344 (Issue 2): –

http://publicapps.caa.co.uk/AANDocs/22416/22416000000.pdf

And here is the AAN for it when it was rebuilt and certain mods removed by ARC for Tom Blair: –

http://publicapps.caa.co.uk/AANDocs/29241/29241000000.pdf

And the AAN for the wing gun bay fuel tank installation: –

http://publicapps.caa.co.uk/AANDocs/29241/29241000100.pdf

Cheers

Paul