It looks like you have already quilted the seams between the blocks? If so, I see a little “extra” fabric in the plain blocks which means you can’t really quilt anything in them that goes from seam to seams or you will have puckers. My suggestion would be to trace one of embroidered tractors on cardboard and use the template outline to mark a tractor you can quilt in the center of the plain blocks. I would also outline quilt the tractors in the embroidered blocks.
p.s. With the difficulty of marking on white, I might use the tractor template to trace the outline on freezer paper several times. You can then iron the freezer paper template on the plain blocks to stick it down to quilt around. If you have use a polyester batt, be careful with your iron though. Polyester batt melts if it gets too hot.
Last edited by Tartan; 08-21-2019 at 05:27 AM.