Indeed it is the same.

There is fundamentally a bigger difference between Bally -17 and -35 boards. The -35 boards support double the amount of ROM capacity which was needed when their games became more complex. Lost World was the first -35 game. This was done by using a previously unused CPU address line in the ROM mix. The extra pin at J5 is that address line (A14).

Bally never made a board with dual battery backed RAM.
Other differences are MPU-200 ran a reset signal to the J4 connector pin 13 that ran to the cabinet slam switches allowing them to remove the slam tilt switch from the switch matrix, an interrupt line was run to J4 pin 11 that was used with their speech board.
Other big difference is the CPU on the MPU-200 boards was run at nearly twice the speed of the Bally-35 board. Stern developed a high level programming language requiring the extra CPU speed.

Note there was a 4th type of Bally MPU board at the end of the run and used on Fireball Classic and Cybernaut. The 6800 CPU was replaced with a 6802, it had a socket for 2764 EPROM and the battery backed RAM was higher capacity. See here:
http://www.pinball4you.ch/okaegi/pro_6802.html

It could be provided you format the ROMs correctly. I've never entertained this downgrade but you would have to program EPROMs accordingly by putting the -17 ROM code into the correct areas of EPROM.
PinWiki discusses the data structure of the ROMs here though it mostly relates to -35 setup:
https://www.pinwiki.com/wiki/index.php?title=Bally/Stern#Jumper.2FROM_Info

Besides the ROMs yes. The type of ROMs will determine if you just need jumper changes or to reprogram replacement EPROMs.

Other than reproduction boards, no. The MPU-200 is the more powerful of the lot. Double CPU speed. Double battery backed RAM. Double the ROM capacity of a MPU-100 (but same as Bally-35 boards).

But you've fixed all his MPU boards and they're 150% so shouldn't fail right
Since you're getting an EPROM programmer you could just send him complete MPU boards that will plug'n'play.
The less he does to the suspect boards (by not removing chips) the better the chance you have of seeing any problem.

The huge number of Bally-35 games produced should present opportunity to use those boards.

You will have to make modifications to the -17 board to make it function like a -35 board. Bally released a service bulletin: F.O. 597 describing the modifications which are rather heavy - note this is for 9316 PROMs only, not 2716/2732 EPROMs.

The service bulletin is attached in this post:
https://pinside.com/pinball/forum/topic/converting-a-bally-17-to-35-mpu-with-fo597-service-bulletin#post-3061345

+1
It comes with some custom ROMs for other games and has the hardware ability to help upgrade to 7-digit displays if your scores get good enough