Howdy ma'am welcome to the group.
I am certainly not an expert, (and no doubt, should I be in error here, someone will step in with more accurate info) but I believe forearms are interchangeable, even though the actual rifles with the 38-55 barrels have a different stock and forearm.
If you shoot with iron or open sights, it is recommended that you do not use a Monte Carlo stock as would be found on your 243. A shotgun type stock, or a stock without the Monte Carlo cheekpiece works better with open sights. I have .357 mag with an aperture sight on a frame with a shotgun stock and a Mannlicher forend that is very comfortable to shoot this way (and I think looks sharp :lol:).
You can see I have the rear aperture attached at the pre drilled and tapped rear scope mount holes. My sight has no target inserts, simply an aperture. Most folks would likely not consider this set up as an accurate long range shooter (and I do not either) but it works well for mid-ranges for me. (100-150 yds)
There are also different sights available for the longer ranges, a ladder type sight, and I've even seen a tang sight that was inletted into the buttstock.
There have been a number of threads about this very subject and can be searched through the 'search' option.
I tried to use it just now, but for some reason I can't seem to access it at the moment, but if you want to use it, check the FAQs and Stickies at the top of this forum and find how to use it (the search) then type in "long range sight" or whatever it is you want to get more info about.
Again, welcome to the group. Lots of great people here with great information.
Cheers
Kerry