Would be interested in your thought process
@Bald Rick?
For me the problem is at Cambridge itself.
The long platforms of most use are on the Upside here. Platforms 1 and 4 have their own restrictions in terms of crossing moves but also overlaps which they share. (assume Platform 4 is 12 carriages by then from this link,
https://www.greateranglia.co.uk/abo...ation-be-extended-make-room-new-longer-trains )
Kings Cross Down services will need to cross at Cambridge to reach Platforms 7/8 if 12 carriages to terminate. Liverpool Street and Stansted down services will need to cross at Shepreth to reach paired by direction lines.
On the Up All Kings Cross services need to cross at Shepreth Branch Jn to head towards Hitchin and secondly those starting from Platform 2/3 will have to cross leaving Cambridge Station to reach Up Lines paired by direction.
I think it might be better for Up Down Kings Cross and Up Down Liverpool Street pairing of lines. Kings Cross services using Platforms 1 to 4 at Cambridge (but see below) and Liverpool Street / Stansted services using Platforms 7/8.
The issue then becomes Kings Cross to Kings Lynn / Ely services which I might well use Platform 4 and attach / detach there in both directions and leave the London End Unit there for the next service. This service group along with Ipswich to Cambridge services would be the only service groups crossing Liverpool Street / Stansted to Cambridge North / Birmingham services at north end of Cambridge.