Rather than drilling two new holes in the steering wheel you could make up two steel bushings that would press into the 3/8" holes and be 1/4" on the inside to accept a 1/4" roll pin. Another option would be to take a 1/4" bolt and turn the head to 3/8" outside diameter in a lathe so that it would be tight in the 3/8" hole in the wheel and put a screwdriver slot in the head using a hack saw. A 1/4" nut could be similarly turned on the outside to match the 3/8" hole in the steering wheel. Install the wheel, bolt and nut using a bit of blue thread locker on the threads so that it did not come undone.
Just a couple of other options you might consider to reuse the original holes. Make sure that you verify the orientation of the holes at each end of the shaft in relation to each other so that your wheel will be centred when going straight.
I like the bushing idea; I'll give that an attempt. I'll give it a try on the spindle first.
Made more progress today. One of the brackets on the PTO rod that runs through the cast steering console is worn from the roll pin that it rides against as seen in the picture, so I needed to get it removed to repair it. First choice was to pound out the roll pin that holds that spacer with the flat-spot on it, but after destroying two punches without moving the pin at all, I opted for plan B: cut the weld that holds the idler pulley bracket on the end of the rod and slid everything off that end. Also removed all 4 tires from the rims; the fronts are pretty bad but should clean up. The rears are clearly newer. I was intending on reusing the tires to save money, but using the old "piece of wood and my truck" method of breaking the bead, noticed that the tire sidewalls are really dry-rotted; 3 tires had tubes.
I then set about removing the spindles from the axle, and the axle from the front cast frame. The pin required several rounds of heat and beat to eventually persuade it, and once it did, discovered that it is worn where it rides on the cast frame, so I'll be replacing that with some round stock along with the steering column. The PTO has a broken ear, and the bolt that would have been in that ear was broken nearly flush with the frame. I hadn't noticed something else until this time, when I tried to remove the axle: the bolt opposite the broken bolt was also broken, but this one was snapped half way through the frame and was sticking out the axle-side of the frame just enough to prevent me from removing the axle. It's exposed threads were also flattened from making contact with the axle over the years. Looking closely, I noticed that someone had attempted to drill it for an easy out, but gave up with the bit wandered, possibly toasting the threads in the frame. I'd intended on welding a nut to the exposed broken bolt shaft (at the broken PTO ear) and hopefully remove it that way, but as I had my torch out, decided to use the heat treatment on both. I clipped a pair of vice grips on the single exposed thread, and much to my surprise, the bolt spun right out! I'd assumed that someone would have tried that in the past, or that the bolt had snapped for a reason, but apparently that reason was not resistance. From its ease of removal, I moved the other side of the axle up as high as it would go, reached in between the axle and the frame with a pair of thin vice grips, and attempted to spin out the bolt towards the axle. It too came right out. Then, to make sure everything was on the up and up, chased all three holes with a tap; actually took several passes with the tap before I was satisfied that bolts will be able to thread in. Lastly, I epoxied the cracked and broken plastic dash (I guess older models had metal?), but unfortunately, the starboard side corner is cracked completely off and gone forever. Who knows, maybe I'll fabricate one out of metal.
Also picked up my paint today; I found a Rustoleum off-white which I will be using where G9s should have white. Breaking from stock, I'm going with a deep blood-red for the wheels like the earlier tractors. For the frame, I was torn between gloss black and metallic brown. In the end, I ended up going with the black, liking the combination of white and black more than white and brown after looking at pictures of both while in front of the paint rack.