You can also have your original M42 main caps machined by Metric Mechanic to accept the early M20 bearings. You get the 360* thrust bearing AND 360* oiling grooves.
It cost about $125 to have the caps done through MM. I have had them do 2 sets for both my rebuilds. I am sure you could find a competent machinist locally to do the same, probably be about the same price.
Oh ya, also you can go with different main caps from a different engine, BUT you will have to have the block line bored and honed. Thats about a $150-$200 operation. And no, I do not know if the M47 caps would work, not familiar with that engine.