You have a really great start. By the photo it looks like your road is already crowned and ditched and is shedding water without erosion. So you have a great base. To get a great surface you either have to remove the big rocks that are present, or cover them over. Picking rocks sucks, but it is far easier to remove something then add, and I think in your situation it would improve a lot of places. Where rock removal still is too rough, you will need to add gravel, and you want fairly small stuff. By the look of your soil you
should have a gravel bank around there somewhere.
Here in Maine, our glaciers ran to the sea which was in a Southwest Direction, therefore gravel is always found on the East side of a hill since that is where piled up and was exposed as the glacier melted. The southwest side of a hill, that is where the glacier scoured away the soil to almost bedrock, so soil is thin there typically. So you will have to find which way the glaciers ran where you live, and check the opposite side of the hill.
Another place to check for gravel is near old cemeteries. Obviously don't dig near them too close, but back in the day when old graves had to be shoveled by hand, the old duffers went where the shoveling was easy and the soil depth was deep.
Check around for an old bank where the gravel for the original road was dug up from. Around here logging roads are built from soil found on site as gravel usually exists somewhere. It might have grown up into old bushes and
trees, but you might be able to find some. If it is not on your land, you might be able to ask to use it. I let people use my gravel to fix up there roads all the time. When they built your road, I am pretty positive they did not haul gravel all that far.
As for the log trick. it does not work. I tried it a few months ago as I began building a new access road on my farm. It works well for smoothing fields because of the light fluffy soil, but on roads it just drags gravel, then "thump": it rolls over itself and end up leaving a VERY wavy surface. This was the reason I fabricated a grader blade for my log trailer...I needed a very flat surface for my road. It has to cut the high spots, and dump the gravel into the low spots to be effective. A log just does not "cut" as it has to on a road way. BTW: 3 point hitch mounted grader blades do not work either as when the
tractor goes into a dip it drives the blade into the ground, and when they go over a hump, it lifts it off the ground. This leaves a VERY rough road surface.
Also, if you use regular soil, it will just slime up when the next rain comes making your road a terrible mess. It does not take much gravel to give a car grip and still shed water, but its gravel and not top soil.
You got a nice meandering road though that many people would die for. Nice property!!