Off topic a bit but with my "lack of washers on my build" being the catalyst for this thread, I wish to chime in an important detail.
A lot of what has been shared so far, explains why my old bolts also had no washers (I pulled out the old baggie of used bolts yesterday as well as looking at my tear-down pictures again)...I have shared this detail before but my engine assembly is a July, 1967 assembly date...long AFTER the change-over time narrowed down so far. All engine-related date codes and visual differences confirmed this (e.g., C8 thermostat housing, C8 timing cover (with a tin timing pointer), C8 casting on the block above the starter, with "302" casting in the lifter valley). Yes, the engine is a replacement engine. This replacement was done in 1986 by me. This 289 was removed from a much lower mileage 67 Cougar A-code car. Little did I know at the time about date codes and change level details that we now know of today.
At the time, I believed it to be a very wise choice to loose over 100,000 miles on my engine. As a matter of fact, it still retains standard bore, standard rod and main journal specs.
(Fortunately/Unfortunately) Today...knowledge of such details are indeed key to helping pinpoint inconsistencies on "Thoroughbred Examples" out on the show field and I am sure, helpful at times of purchasing a classic Mustang (as well as any Classic car). These details are indeed very helpful in discovering the truth. I truly enjoy learning about these nuances and mind-blowing details.
That all being said, I am not building a Thoroughbred example nor are there any plans to sell the car (even after my passing) so as such, I also have no plans to "throw the baby out with the bath" either. This is an excellent engine assembly with the only defect being that it was "born about nine months too late". The decision was made several years ago to keep the "incorrectly dated engine" so having no washers on a July 67 assembled engine, is if nothing else, consistent with the final assembly date codes of the block, heads and exhaust manifolds.