We offer a modfied adaptor with a radiussed exit and slightly larger ID.
We don't know where to get the filter adaptor with the external wrench flats. Ford stopped using them about 40 years ago. They were used on the 1968-1970 engines (not all 1970 model engines have them as this was the year of the changeover to the round filter adaptors).
We considered making the wrench flat version ourselves but feel that the Performance Filter Adaptor that we currently offer is a better part. This is because the wrench flats protrude above the block and interfere with the flow of the oil around the filter pad's circular cavity. Also, while the OEM ID is 0.500", the current version that we offer has a nominal ID of about 0.512" which offers greater structural integrity than a modified .5625" diameter does while providing significantly improved flow characteristics over the standard 0.500 ID oil galleries of the OEM passenger car blocks (5% greater volumetric capacity than the rest of the 0.500" ID downstream galleries). The current Performance Filter Adaptor, combined with the passenger car block oiling mods as outlined in the Technical Pages of our website, has been proven to offer more than adequate oiling capabilites for engines generating literally thousands of horsepower.
Our specially prepared oil filter adaptors have a radiussed exit so that oil can get around the hard corner easily and keep the downstream oil pressure better replenished. Also, by flaring the exit oil flow slows down as it enters the block cavity which reduces turbulence in the cavity and helps prepare it for the abrupt turn.

Another nice feature is that our adaptor's block threads have a shoulder at the top (blue arrow) so that it cannot be screwed too far into the engine block and bottom out/cause a restriction unto itself (works like the shoulder of the wrench flatted version, but without the restriction of the wrench flats). And the block threads are not too tall (orange arrow) for the same reason.

We include a 3/4-16 nut to facilitate installation. Instructions included.
For details, click HERE and scroll down.
Paul
p.s.: Enlarging to 9/16" is just way more than necessary in most every case; this is true for sure with the passenger car block.