Back in the day the preferred approach was to attach a sling swivel stud to the front barrel band. This was done b drilling and tapping the for end for a swivel stud, but since you only have about 2 threads worth of purchase, the stud was also welded to the barrel band, ground smooth and the weld cold blued. It's a lot stronger than inletting the forend for a blind nut.
Today, you can buy Model 94 barrel bands with the stud already attached.
I won't say Winchester never added sling swivels to a Model 94 carbine, since Winchester would do pretty much anything on a custom order basis. But generally speaking, Winchester only put sling swivels as an option on rifle and short rifle pattern Model 94s. The front swivel was attached to the end cap (since rifle and short rifle Model 94s don't have a barrel band). The rear swivel was attached to an inletted base plate secured by two screws.
Below ae a pair of pre-64 Model 94s and you can see the after factory front swivel stud on the upper Model 94, as well as a regular screwed in rear swivel. It'll affect the collector value of a pre-64 Model 94, but not all that much. Personally, I like the way the Model 94 carries in the hand, but if you want to add a sling, I wouldn't worry about the slight hit in value, especially if it's in less than excellent condition anyway.