This is the only way I can see it working for Hourly Cambrians
Down
0625 Birmingham New Street - Aberystwyth 0920 (Shrewsbury arr 0718 - dep 0727)
0708 Birmingham International - Llandudno 1030 (Shrewsbury arr 0819 - dep 0821)
0740 Wrexham General - Aberystwyth 1025 (Shrewsbury arr 0820 dep 0827 ) *
0808 Birmingham International - Aberystwyth (front) 1125 & Pwllheli(rear) 1310 - (Shrewsbury arr 0919 - dep 0921) - Splits at Machynlleth
0908 Birmingham International - Holyhead(front) 1313 & Aberystwyth(rear) 1225 - Splits at Shrewsbury. Front portion departs 1023, rear at 1027
1008 Birmingham International - Aberystwyth(front) 1325 & Pwllheli (rear) 1510 - (Shrewsbury arr 1119 - dep 1121) - Splits at Machynlleth
1108 Birmingham International - Holyhead (front) 1508 & Aberystwyth(rear) 1325 - Splits at Shrewsbury, Front dep 1222, rear 1227)
etc etc
UP
0518 Shrewsbury - Birmingham International 0650
0633 Shrewsbury - Birmingham International 0750
0514 Aberystwyth - Birmingham International 0850 (Shrewsbury arr 0711 dep 0733)
0515 Holyhead(front) & 0630(rear) Aberystwyth - Birmingham International 0950 - (Shrewsbury, front arr 0824, rear arr 0826, dep 0831 for Birmingham International) - Note: Another 158 will be required for the Wrexham to Aberystwyth through service.
0646 Barmouth(front) & 0730 Aberystwyth(rear) - Birmingham International 1050 (Shrewsbury arr 0926 - dep 0933) - combines at Machynlleth. **
0830 Aberystwyth(front) - 0715 Holyhead(rear) - Birmingham International 1150 (Shrewsbury, front arr 1026, rear arr 1029, attach then depart 1033)
0720 Pwllheli(front) & 0930 Aberystwyth(rear) - Birmingham International 1250 (Shrewsbury arr 1126 - dep 1133) - combines at Machynlleth
etc etc
Notes:
*This service used to join the 0831 to International, but instead operates as a through service to Aberystwyth. Runs 7 minutes earlier to provide a connection with a Birmingham Service and to enable the driver to change ends. 0700 Shrewsbury to Wrexham Service will become the 0653 as a result.
**This is the current 6 car 158, subject to change.
That Pattern would work quite well until the 1919 off SHR, where it would revert to how it works now. It would require 2 more 158's however.
Also, ECS moves have not been included.
I have added the full station names and take out the head codes. I have also highlighted in Bold where the changes are