To the extent I've looked at it, without reading original documents, the original OoO design that current systems are based on, the IBM System 360/Models 91 and 95's floating point unit using Tomasulo's algorithm https://en.wikipedia.org/wiki/Tomasulo_algorithm didn't extend to speculative execution.
No doubt because gates were dear, implemented with discrete transistors, and that processor was a vanity project of Tom Watson Jr's. And memory was slow, core except for NASA's two 95's with 2 MiB of thin film memory at the bottom, and cache was still a couple of years out, introduced with the 360/Model 85. OoO becomes compelling when you have a fast and unpredictable memory hierarchy, as we started to have in a big way in the 1990s when we returned to this technique.