The mid-'60s also saw the contraction of the Southern Region's activities in the far south west of England, resulting in the WR gaining a much higher route mileage with a territory now stretching from Penzance to Salisbury. This western expansion caused the use of 116 units on long distance services for which they were considered unsuitable, due to their lack of toilet facilities, to remedy this situation seven Laira hybrid sets were assembled at Newton Abbott, this involved the substitution of the Class 116 DMS cars with those of Swindon built Class 120 units. The latter of course being equipped with toilets in both the DMS(L) and the TS(L) vehicles. This operation resulted in both the 116 and 120 sets being equipped with one toilet in each type of 3-car set treated, long distance passengers travelling in what was essentially a 116 set needed to make sure they rode in the appropriate vehicle as at that time there were no gangway connections fitted to class 116 vehicles. They were now mainly based at Exeter, and worked on some of the longer ex-SR lines such as Exeter to Padstow, Bude, Ilfracome and Plymouth via Okenhampton as well as the former GWR routes to Kingswear, Paignton, Torquay and Plymouth.
When these sets were disbanded all but two of the original DMS cars were returned to their correct sets, the two incorrectly paired remained that way until their eventual withdrawal in the late 1980s.
The swaps were:
| 50898 from | LA 300 leaving | 50845 / 59362 | with | 51585 | (from LA 504) |
| 50902 from | LA 301 leaving | 50849 / 59357 | with | 51586 | (from LA 505) |
| 50918 from | LA 302 leaving | 50865 / 59372 | with | 51583 | (from LA 501) |
| 50871 from | LA 310 leaving | 50818 / 59326 | with | 51589 | (from LA 506) |
| 50921 from | LA 311 leaving | 50868 / 59326 | with | 51590 | (from LA 502)* |
| 50877 from | LA 312 leaving | 50824 / 59332 | with | 51588 | (from LA 507) |
| 50900 from | LA 313 leaving | 50847 / 59353 | with | 51582 | (from LA508) |
*51141 (from LA 303) was exchanged with 51590. However, as LA 303 had a lavatory (it was power cars 51128/41 with Class 118 59481) 51590 changed with 50921 in LA 311.