Is it possible to recover / convert / mount fakeraid image files? (TL;DR - have fakeraid images, want to convert them to mdadm images)

I found my self in the same situation. I was able to recover the data using the demo version of R-Studio to reconstruct a virtual RAID array mostly as described here:

https://www.r-studio.com/automatic-raid-detection.html

Under the "Drive" menu, select "Open Image" and import the drive images previously created using dd.

In the "Create Virtual RAID" drop down menu select "Create Virtual RAID & Autodetect", then drag and drop the opened drive image files from the tree view (on the left) to the virtual RAID device list panel (on the top right).

Click "Auto Detect". The process should complete in a few seconds. In my case it detected a 32k block size, RAID5, Left Async (Continuous) with 50.2% confidence. It also displayed the text book diagram of a RAID 5 array. Click "Apply".

Back in the "Device view" tree, there should now be a partition and volume group (e.g.: "vg002-lv001") with an ext3 file system. Select this entry and click the "Create Image" button.

In the resulting dialog box, select "Byte to byte image", choose an appropriate path and file name. Click "Ok" and then wait overnight for the process to complete. Make sure you have enough room for the resulting image. (For 4 x 500 GB drives in RAID5 that will be approximately 1.5 TB.)

The resulting image file can be loop mounted to access the data. E.g.

# mkdir /mnt/promise
# mount -o loop vg002-lv001.img /mnt/promise/

I also found it convenient to remap the UIDs and GIDs before running rsync to copy the data:

# mkdir /mnt/promise-bindfs
# bindfs --map=1001/1000:@499/@100 /mnt/promise /mnt/promise-bindfs