Yeah Rob, that looks like the point where 55/late 30's had the seatbelts bolted to.
Are you wanting to put later model seats (55/late 30) into your 30?
You can actually mount the early 30 seatbelts stalks onto the side of the later seats (there's a hole in the seatbase, that is covered by the upholstery, which works fine.....although holding the nut on inside can be a bit tricky).
I had KE55 front seats in my '74 KE36 and used the original style seatbelts with no problems at all.
Cheers
Dougy
:)