Low pressure .45ACP loads
SAMMI pressure standards:
.45 ACP 19,000 cup or 21,000 psi
.45 Auto Rim 17,000 cup
.455 Webley Mk. II 16,000 cup
You are correct stating that the .45 ACP has a higher allowable pressure than the .45 Auto Rim and the .455 Webley Mk II (the caliber your pistols were originally chambered for).
Modern Reloading by Richard Lee has several pages of .45 Auto Rim loading data and indicates the pressure of those loads which will provide you with acceptable reloads in a safe pressure range by loading the.45 ACP with .45 Auto Rim data.
Also check Hodgon's Reloading Data Center for 230 grain loads for the .45 ACP that are in an acceptable pressure range for your pistol. There are probably numerous other internet sights that can provide loading data for pressure ranges in the 16,000 cup range.
Using .45 Auto Rim data for loading .45 ACP cases is not a problem since the case capacity of the .45 ACP is 22.87 gr's of water and the .45 Auto Rim capacity is 22.92 gr's of water per The Handloaders Manual of Cartrildge Conversions by John Donnellly.