The Mr. Wizard’s Experiments In Electronics III model was sold starting in 1974.
The Electronics III model is very rare and I have not seen it any eBay auction since I began the Lectron.Info project in 2012. I was only able to find it listed once in a completed Craig’s List sale from October of 2012. Only the cover photo was available from a cached page. I therefore have no layout photo to offer on this page.
In December of 2015, I was able to purchase the Mr. Wizard instruction manual for this model.
I cannot be certain as to how many blocks were in the Electronics III model because of the possible duplication of blocks. We can see however that the block types more closely match the Electronic (I) model with the exception of the added 10K Ohm and grounded component substitution blocks.
The experiment count did rise to 55 but due to the missing tuner block and several other blocks that the Electronics II model had, the diversity of experiments was narrowed. Unfortunately, the Electronics III manual did not provide a table of contents for the experiments either.
The complete instruction manual may be viewed/downloaded from the Kimble documentation page.