This is a 74 G?
 

Sure doesn't look like one.

https://skymaster.com/product/1974-cessna-337g/

Data shows as
1967. 337C
337-0786

The giveaway is the rear side window design. On the "G" models, all the side windows are rectangular, but on the earlier models, the rearmost side windows had a bit of a slant to them.

Here is an example of the earlier rear window style:

Attachment 3083

I would think the automotive style door, the fixed step, and the low data plate number would be a hint.

1966- 1972 Have regular door
1973 on have clamshell door