Recovery of iPhoto Library originals?

I'm attempting to recover lost photos from an overwritten MacBook Pro hard drive. An iPhoto Library file is intact, migrated onto another MacBook Pro, but when opened in iPhoto – or imported into Photos – displays numerous missing images. Having spoken with Apple iPhoto app tech support, I understand that the original images seem to have been erased. This support tech mentioned that once the complete (original/lost/overwritten) library file is found, Apple app experts like himself are able to render the images recoverable.

I'm trying ProSoft Engineering's Data Rescue (v. 4.2, Free Trial) on the overwritten drive. I was told by my iPhoto tech that the average person's library file size is between 4 and 7 GB, and to look for a file size around that size. A 'Deep Scan' (for deleted files and erased drives) generates a lot of .jpg files, but I reviewed them, and none are the photos I'm looking for. However, there are two .rsrc files (with alphanumeric filenames that seem to have been assigned by Data Rescue during the recovery scan?) that are both 4.2 GB. The Data Rescue Free Trial only allows recovery of files up to 2 GB, so I'm trying to determine whether this is the right file, and the right software for the job. Can anyone shed some light?