I think you’re simplifying the advice given on what would make a fowler look earlier.
There will be lots of viewpoints on your current question. There are very few existing rifles made in the colonies that appear like what some of us think rifles made here in the 1750s should look like. Usually it boils down to 3 or 4 categories of features.
First is architecture. Does it look like a slim Golden Age longrifle? Then it doesn’t fit the 1750s period if it has Germanic styling. The Woodsrunner does not typify strong Germanic styling. We typically want a wide, tall buttplate with almost zero curvature on a very early colonial rifle. Often a wide toe. If Germanic in styling we want a bold cheekpiece that may protrude almost as much at the front as at the rear. Reference these guns which fit my conceptions, though not necessarily dating to the 1750s: the Marshall rifle, the Tulip rifle, the Musician’s rifle, RCA19, and the Natty Bumpo or James Fennimore Cooper rifle. If English in styling, it’s hard to say. Look up the Turvey flintlock English rifle. Obviously you can’t change the architecture on a pre-shaped kit gun to make it more robust.
Second is furniture. The buttplate is mentioned above. Some early Germanic style rifle guards have the grip rail well off the wrist, and some have front and rear extensions with interesting finials instead of being squared off. On a gun with English influences, it’s harder (for me) to point to an English guard for a rifle and say, “that one sure looks early to mid 1700s!”
Third is parts. The barrel and lock should be readily similar to documented barrels and locks from the period - or EARLIER as many guns in the early days appear to have recycled parts. Those cannot be changed on a kit gun.
Lastly one could theoretically employ carving that is off an earlier colonial-made gun - and there are zero to one rifles surely made here with reliable dates placing them in the 1750s.
I’d advise being happy with your gun as it is, and getting or building an earlier gun if that’s what you really want.
Hoping others will chime in on how they would approach your situation. Feel free to PM me.