That would be a down-grade.
You could ask Henry if they know of a source. They have probably considered plastic as a cost-cutting alternative or option at one time or another.

Cheezywan

 

A friend of mine put a very well-crafted, tang-mounted peep sight on his Henry 22 lever gun. His accuracy improved without detracting from the beauty and clean lines of the gun.

I cannot imagine making any other changes to that gun that one could call an improvement. I tend to agree with Cheezywan, that any other change would be a down grade. YMMV

 

Hi Viz sights will not shoot as accurately as a flat black sight will on your gun. You won't find any target shooters using those types of sights for target shooting. They are good for shooting game in hunting situations if the distances aren't great and the animal is large enough to not require precision shooting. For me, they are out of place on a rimfire rifle or handgun that would be used for any type of hunting. I'd go with a flat black front and a peer rear sight.

 

Think twice about a synthetic stock on a classic gun. I could understand a wood upgrade if yours came with marginal wood, but not synthetic.

There are some cool peep and ring sights that would stay with the character of the gun. Check out Skinner sights for something that would look appropriate the your Henry.

 

The wood is the best part of a Henry rifle and they already improved the sights, the current metal ones are FAR! cry BETTER than the POS plastic ones they use to put on them, the paint was chipping off of the potmetal receivers for a while, and the replacements they sent out to replace those had horrid "orange peal" paint on them!, they may have that sorted by now?

 

My wife bought me the Henry Frontier to get the better sights and she knew I liked the octagon barrel. The receiver was very orange peeled and I scratched it early in the time of owning it. I took my cover and barrel band off and stripped the finish off and I like it better than the black that came on it new. I have a Leupold 2-7 rimfire scope on it now and not the longer scope pictured. Looks better with the smaller scope.

 

I second the skinner sights. they make a fine product.