If they do still come to Northern despite 7car being an issue he's my thoughts on how they could possibly do things;
Liverpool routes
liv-wgn 5[4x331]
liv-bpn 3[4x331]
liv-mia 3[6x350]1[6x331]
liv-mcv 1[3x331]
South Manchester routes
man-cre 5[4x350]
man-sot 3[4x350]
man-ald 2[4x331]
man-hdf 3[4x350]
hdf extra 1[4x350]
mac extra 1[4x350]
hzl extra 1[4x350]
North Manchester routes
bpn-mia 8 4[6x350]4[6x331]
wgn-mcv 2[3x331]
Total=39
3[3x331]; 10[4x331] ; 17[4x350]; 5{10}[6x331]; 7{14}[6x350]
350x3 60m 14 of 17
331x3 72m 13 of 15
350x4 80m 14 of 17
331x4 96m 10 of 12
Key four Blackpool to Manchester Airport using 331x6
BON 0722 1Y53 = MCO 1637 1N52
BON 0753 1Y54 = MCO 1706 1N53
BON 0822 1Y55 = MCO 1737 1N54
BON 0854 1Y56 = MCO 1806 1N55
Platform extensions to 120m for the 6x 350s on the Liverpool to Manchester airport
Wavertree technology Park platform 1&2, Broad Green platform 2,Roby platform 3&4, Huyton platform 4, Whiston platform 1&2 and, Earlestown platform 2.
There are a few 117m one but you could probably get away with them.
Alternately the 6 car 350s could be deployed on the Liverpool- Blackpool which only require extensions at Euxton Balshaw Lane.
Would also be nice to have the extra 3 to cover Wigan to Stalybridge when that eventually happens.