1600 engine issues Help needed

[something wrong]

Posting this to help a friend out, if you could help or suggest a fix would be great.

This car’s getting the better of us.
Mk1 Escort 71 with Capri 1600GT Kent X-flow engine, stg1 cam, extractors, 40DCOE on 2-into-4 Lynx Manifold.
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Starts fine but only runs on 2 cyls (1 + 3)!!!
No action on cyls 2 + 4, you can pull these leads off and nothing changes when running.
Pull off 1 or 3 = almost dies.
Plugs 2 + 4 = still completely clean (all are new yesterday), Plugs 1 + 3 = already light tan/dk-grey
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Firing order is 1-2-4-3 (=std all Eskys)
Inlet manifold = 1/4 + 2/3 (ie 1 choke of DCOE => 1+4, other choke => 2+3)
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Done all the following:
Compression check (140/160/140/140 – approx)
New plugs leads
Leads + plugs switched around
Points / dwell set @ 40deg
Timing set @ 8BTDC
Timing light put on each lead = good flash
Plugs 2 + 4 pulled and earthed = good spark
Carby disassembled, blown out, level set, idle set, etc. Tweaking idle on each choke =
Valve clearances set, top-end looks OK, nothing sticky
Dizzy checked (cap/rotor/no shaft wobble/ vac+mech advance OK)
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Err, have we missed something?