The Radial lower mast is not a cut-down Standard lower. They're different sections, and the Radial is considerably softer. I wouldn't expect a Radial sail to set well on a shortened Standard mast, and you may very well end up with the old "M" rig problem: the mast being so stiff that it negates the difference in sail areas.
There should be cheap aluminium Radial lowers available now that many have switched to carbon. Ask the top Radial sailors in your area.
(Or stick to the Standard rig. Doesn't matter much if you're really not racing.)
Yes, you can cut down standard section and sail the boat with a Radial sail. But no, it will not work.
The Radial spar is made from thinner aluminum to have a specific bend characteristic that matches the Radial sail. A sawed-off standard spar will be too stiff, and the mast will no bend properly in a breeze. This will make the boat harder to sail, maybe even harder than a standard sale/spar combination.
Torrid, have you tried it?
I have; I sailed quite a bit with a cut off standard mast.
A proper radial section works better of course but I didn't think we were talking racing.
For playing around a cut off standard section works fine. Save your money and go sailing.