For older machines I always recommend to cover the feed dogs if they don't lower. I use a piece of thin plastic. Cards will work if in an emergency and I can't find the plastic. Also on older machines to dial the stitch down to 0 so the feed dogs don't move. I don't want those dogs chewing on the bottom of the quilt.
I know some don't drop the feed dogs and leave them moving and it works, but I want to disengage as much of that mechanism as possible and make the surface smooth. I have found that in some cases because of the printing process that the color/dye can be scratched off the lining. Better to be safe than disappointed. Just punch a hold in the card or plastic. I had a case one time when a student brought a featherweight in and the cover to the bobbin was left at home. We just taped a card over the area and it sewed fine.

If you can dial the stitch length to 0 that would be the best way I think.

Yes, stitch length to zero with feed dogs up! Some older machines will work better for fmq this way. Leah Day's website has lots of info. and designs for fmq. Good luck and practice!