The earliest production units from fall of '57 had Sony oval transistors in them, but Standard moved to Hitachi ovals by the end of the year. (Not surprisingly, this timing coincides with when Sony stopped selling their oval transistors to other makers.) The grey unit pictured on the left uses Hitachi transistors, but the internal layout is otherwise the same as the ones from earliest production; this radio looks to have been built around January 1958. Within a few months the company revised the circuit board and you can see the newer version inside the green unit pictured on the right. One easy reference is to look at the transformer on the right side and the relative positioning of the pair of transistors located beside it. The transistors and diodes themselves are the same as used in the earlier grey unit. This green SR-F22 looks to have been built around May of '58. As an aside, I have the original bill of sale for the green unit; it was sold in Oregon on September 11, 1958.
Transistors: (Hitachi) HJ-23 x 1, HJ-22 x 2, HJ-15 x1, HJ-17 x 2, [1N34A]