I found here an Allison transmission parts manual that includes revision modifications for the following;
SUBJECT: All-Range Lockup Conversion Requirements for the HT-700 Transmission
The all-range lockup feature has been released to the HT-750 DRD and will be incorporated into all HT-750 DRD units at the start of Model Year 1976.
Transmissions with and without retarder or engine driven PTO option will have this feature.
To incorporate this change on 73, 74 and 75 Model Year transmissions in field service, three (3) Conversion Service Kits have been released and are available.
Kits released for conversion are:
Kit P/N 6881215 for Model Year '73 Conventional Models;
Kit P/N 6881216 for Model Year '74, '75 HT-750 DRD High Torque Rise Models,
Kit P/N 6881217 for Model Year '74, '75 HT-750 DRD Conventional Models.
As similar as the 740 series models are I wonder if this is the way to go when modifying the transmissions in most coaches.
The revisions start on page 492, where the revision I am referring to starts on page 516.
The link is to a military TM:http://www.liberatedmanuals.com/TM-5-4210-227-24-and-P-4.pdf
More manuals (4000+) can be found here:http://www.liberatedmanuals.com/