Seat covers

I wonder if any of you good people could help me. I have I think 2 country seats and have got covers the bases fit fine but the backs on mine have a plastic cover and no vinyl where as the new ones are complete both front and back and so
A. Not sure how to do them up as there is no channel for the metal rod on the front part to hook underneath and connect on to the hooks like the base does.
B. I guess I can’t now fit the back as it covers the side channel where the plastic slots into along with the trim bead. Here are a couple of pictures. The first being the old cover. TIA
Chris

Oh and here’s a picture of them from the front. They look quite nice. covers are Britpart and I will paint the frame.

Seems a shame to cut the new ones. Can you cut a (say) ally strip and screw it to the seat frame?

Prefer not too

The wife thinks we could possible stitch them together using thick thread, but was wondering what the proper was was.