I fitted 850 seats in my 544.

I connect the electrical seat controls directly to the battery as I almost never adjust the seat. (Plus - I'm lazy)

I had two 1/2 X 3 inch bars welded to the seat rails after I ground off the original mounts, I also found out that the seat frames had about 3 inches of height adjustment.

When I was done, I found that I could have saved the side air bags as the are not electric.

I made a 1/2 inch piece of plywood, mounted it where the 544 rails were and bolted the seat bars to the wood. I cut out the back and the front to form sort of a fat H - when I was satisfied with the configuration, I copied the wood in 1/2 inch aluminum

Tips

Seats are supply and demand at the junk yard - some modern seats are cheaper than older ones

Pick a donor car that has intact weather protection.

Cloth seats are nice if you have no AC

I should have taken the back seat as well as it could have been narrowed to fit.