burned a bunch of propane with the floor heat turned up yesterday and have a general idea of the layout in the slab. It's not super easy to see them, there's only a 5-10F at most difference.
There were no warm spots near the axle rack at all, so looks like I lucked out. I'm surprised at how far apart they seem to be. I wonder if some of the lines could be plugged? Was hard to see the return manifold temps with the hot of the feed manifold tight behind it right there.
camera is slow to update and low res but seems to do its job. For the price, would be nice if it were nicer but that seems to be what is. I saved a bunch of shots, will upload sometime.