this is actually Hemimarks out of his Hemi Barracuda. I sent Bro John some pics of a stock shaft also....maybe he will post them
when I disassembled the steering shaft assemby, the original builder, had simply machined a flat side on the 3/4"od round shaft and used a saftey wired 3/8" bolt to hold it in place. Thru time, the bolts had created slop / play in the column.
I took the the factory shaft to my fab guy and had him...
1) machine for DD shaft
2) machine a slot for the set screw to eliminate the adapter / universal from slipping off.
for most installs, simply cut the shaft after the pin hole for the rag / vibration joint. you can also shorten up the shaft if it works better for your motor/ exhaust combination. Try to keep the universal as straight as possible with the least amount of angle in it.
I think this is most cost effective and safe way to adapt to your 3/4" round factory shaft