The 7591 is electrically similar to the 7868 but has a different base. Coletronics published settings for the 7868 and if they are accurate this data can be used to create settings for the 7591. The attached image shows my best guess for 7591 settings based on data for the 7868 and 6L6.
Attachments
After further scrutiny the F column should have a letter with the numbers to set meter shunt, plate load and plate voltage. The manual does not define what each letter signifies for those parameters so try it with 046Y, similar to the 6L6 setting.