If you can, def. use the frame as the jack stand point. Was not easy when I placed the axle pivot seals but it is doable.
I have been getting antsy while I wait on my spacers to arrive. I did a test on the location I was planning. Those old jack stands fit the frame nearly perfect. I found that it's practically impossible to only jack one side of this tractor off the ground and jacking on either side of the draw bar will lift both sides but unevenly. Jacking in the center lifts up both sides evenly and everything seems stable with a stand under either side of the frame. I also have a set of newer stands like the one shown in the video I linked to, I plan to put these under the axles after I take the wheels off, these stands with the larger curved support on the top would be extremely hard to place under the frame. I also have wheel chocks for both front wheels. I don't believe that you can ever be too cautious. In my life I have seen all kinds of jacks and I've seen them all fail in one way or another, luckily without any disastrous consequences, and I hope to keep it that way.
Now if those spacers would just arrive.... It's going to be a sunny day here on Saturday, cold, but sunny.
I will try to post some images when I do the work for others interested in these wheel spacers for this tractor, probably in a new thread though.