Just had a quick look at the info I have on the Maunsell Coaches. All the Slaters kits are 9' wide / restriction 4 types of the first high-window variety (previous builds had lower height windows on the corridor side). The Slaters kit has alternate parts for the single vents above the lav window on early builds and the double vent on later builds - the window was the same. On this basis I think the coaches you can choose from are as follows:
6 Compartment Brake Second - Diag D2102/D2110
Note the only difference between the two diagram numbers relates to the internal door to the guards compartment. D2102 is hinged and D2110 sliding. Bizarre that this generated a different diagram number!
92 coaches fit the kit made by Slaters:
2754-2771 (18no / 1932 / 2 lav vents)
2793-2805 (13no / 1932 / 2 lav vents)
3732-3749 (18no / 1930 / 2 lav vents)
3750-3758 (9no / 1932 / 2 lav vents)
3771-3800 (30no / 1933 / 2 lav vents / D2110)
4083-4086 (4no / 1929 / 1 lav vent)
7 Compartment Composite - Diag 2301
60 coaches fit the kit made by Slaters:
5171-5172 (2no / 1929 / 1 lav vent)
5634-5651 (18no / 1930 / 1 lav vent)
5652-5691 (40no / 1932-33 / 2 lav vents)
6 Compartment Brake Composite - Diag D2401
62* coaches fit the kit made by Slaters:
6575-6604 (30no / 1929-30 / 1 lav vent)
6643-6674 (32no / 1930 / 1 lav vent)
*Total number confused by some renumbering
Hopefully this tallies with your own scribbled notes. Most of the above spent their lives either in sets or loose on the western section (ex LSWR), there are a few that wandered a bit more widely.
Set Numbers
A complex subject and none of the reference sources have the full history of all the set changes but the SEMG lists give the following appear to consist of the appropriate coaches from the above lists:
203 London to Weymouth
221, 222, 224 Waterloo to West of England
223, 232 Plymouth to Portsmoth
225-231, 387, 456 London Bognor Chichester
241-250, 327-330 Western Section Local Services
962 Eastern
Gould gives much more detail and identifies that a few more of these sets moved eastwards.
241-250, 237-330 are described as working Waterloo-Bournemouth-Weymouth services by 1951 but downgraded to local services by 1956.
241 moved to the central section for Oxted and Redhill services by late 1959 and was joined by 327 in 1962.
In the 1953 CWNs the allocations of the appropriate (to you) 3 coach sets were:
3-sets B 221-32, 387, 456, 962 London-Margate-Ramsgate-Dover-East Grinsted-Tunbridge Wells West-Brighton-Lewes-Eastbourne
3-sets M 203, 241-243, 245-250, 327-330 Waterloo-Bournemouth-Weymouth, Waterloo-Basingstoke-Salisbury, Waterloo-West of England
In 1956 3-set 330 was damaged in an accident at Bournemouth West.
By 1957 the vehicles from 3-set 223 were used in 9 coach set 455 and 3-set 456 was strengthened to 8 vehicles.
In 1959 the following 3-sets were withdrawn: 225, 243, 328 and the following disbanded: 221, 231.
In the 1960 CWNs the allocations of the appropriate (to you) 3 coach sets were:
3-sets M 242, 244-250, 327-329 Western section local services
3-sets T 203 Ramsgate-Hastings-Wolverhampton
3-sets T 222, 224, 226-230, 232, 241, 387, 962 London-East Grinsted-Forest Row-Tunbridge Wells West-Brighton-Eastbourne, Reading South-Readhill-Tonbridge
In 1961 the following 3-sets were withdrawn: 222, 224, 226-228, 456, 962
In the 1961 CWNs the allocations of the appropriate (to you) 3 coach sets were:
3-sets M 242, 244-250, 327-329 Western section local services
3-sets T 203, 229, 230, 232, 239, 241, 387 London-East Grinsted-Forest Row-Tunbridge Wells West-Brighton-Eastbourne, Reading South-Readhill-Tonbridge-Brighton-Horsham
In 1962 the remaining 3-sets were withdrawn: 203, 229, 230, 232, 241, 242, 244-250, 327, 329, 387.
Loose Brake Composites
Most of the D2401 coaches were allocated to sets but the following were loose at various stages:
6578, 6582, loose from 11/59
6588 loose from 6/62
6595 loose from 4/61
6598 loose from ?/62
6601, 6604, 6645, 6647, 6663, 6665, 6671 loose from 6/62
6643 loose from 4/61
6644, 6/61 loose from 6/61
6646, 6655* loose from 11/60
6661 loose from 6/60
6672 always loose
6673 loose from 2/61
*only in a set from 9/60 to 11/60
So 6655 and 6672 appear to be the best bet.