I am soon to be in this same situation. How does the other type rated captain "attest" to you flying PIC for the 25 hr limitation? Does he sign your logbook, or just write a letter that you carry with you when you take your logbook to a FSDO after the 25 hrs have been complete?
At my previous charter job, all our FSDO required was 25 hours of SOE, and our SOE forms with the Check Airman's signature. But my company did things differently the others. (obviously)