I do not see an oil filter or oil filter mount on the tight front side of the block. If it is actually not there, then the filter mounts to the intake manifold and it is an earlier F engine. I also do not see an oil fill tube on the right hand side of the engine, so it is not a very early F engine either. I am going to guess tht the filter is not installed and the oil filter mount just does not show up well in the picture.
In the NA market Domed pistons were introduced in the '74 model F engine along with the open chamber head.. Some of the last '73 model rigs has this change too. The 2F had domes and open chamber heads until 1981.
I *have* seen flat top pistons in an early 2F with an OPEN chamber head. This was a SA rig, so that may have been a Toyota thing to lower compression for that particular market, or the pistons may have been replaced at some point in the rigs life.
Prior to the '74 model (and again some of the later '73 rigs) the F engine used a brass oil line that snaked up from the block though the oil drain back holes to get pressurized oil to the rocker arms. In the last of the F engines and in the 2F engines the oil flowed through an oil gallery that came out the top of the block and dead ended. From there an brass ring reinforced opening in the head gasket allowed the oil to flow to and through the head bolt bore (the one just behind the dipstick) to reach an intersecting gallery in the head and flow to the rockerarm pedestal.
I can not see if that oil bore is there, because while it is a 2F head gasket, you have it on backwards.
I have never seen a head gasket for an F series engine that did not have a tab at the back end which prevents it from being installed backwards. Perhaps I have just forgotten something I might have seen years and years ago. You did not cut the tab off did you?
Admittedly being a bit pendantic, but there is not a "1F" engine. Toyota called it an "F" and there was no reason to call it a "1F" as it was the only F engine that existed .
When the 2F came along, the F was no longer made. So we have F engines and 2F engines.
There is not a "1.5F" engine. About 20-25 years back or so, people online started calling the 1974 model (and actually a very few of the 1973 model) F engines "1.5 F". I guess it made then feel special? The final evolution of the F engine had all of the early 2F internal upgrades except for the slightly larger displacement but Toyota did not give this evolution a separate designator, just like they did not change the designator at any point when earlier upgrades and evolutions of the F happened over the years.
The F155 sticker appeared on the valve covers during the last couple/few years of the F engine run, but any claims of that representing 155 horsepower are... thin at best
Mark...