Look on page 271 in 65-69
Chevrolet by the numbers for the correct pan usage. Not sure when in late 67 the second pan was put into production, but some time around July is indicated in fig. 15-22. Maybe someone with the
Chevrolet Service News article could supply info.
Also on page 272 fig. 15-23 shows the filter that was used with early pan design.
Bob