Details & Changes.
7, 6 and 5 rib inner pressings- change date?

The reinforcement plate above the chassis rail in the front inner wing started with 7 reasonably equally spaced ribs, up to chassis number 20-014118, or lower. At chassis number 20-014685 the middle of the seat base was changed, relocating the heater control knob and choke lever. This panel then fits against the reinforcement plate where the front rib is located, so this rib was removed.

Highest chassis number know with 7 ribs	20-012086
Lowest chassis number know with 6 ribs	20-014119
Highest chassis number know with 6 ribs	20-020427	Should be 20-019497, as the first ambulance was 20-019498.
Lowest chassis number know with 5 ribs	20-025153

The reinforment plate with 6 pressings.

With the introduction of the VW Ambulance at chassis number 20-019498, the centre section of the seat base was revised to allow for the location of a vertical spare wheel recessed in to the bulkhead. This used a front middle seat base section simply reversed. When this fitted against the reinforcement plate it again became necessary to remove a rib to allow this panel to sit flush. The same reversed front section was also used with the introduction of the single cab. The change from 6 to 5 ribs is between chassis numbers 20-020427 and 20-025153.
On the picture above it is easy to se why the reinforcenment plate was changed over the years.