That bushing is to put an early small hub transmission in a large hub 68 and later slant 6 or a small hub 273 transmission in a large hub 318,340,360 crank.
Which is exactly what he's doing. A '65 Valiant with a ball and trunion 904 that's getting a 340. ALL 340s were large pilot cranks, since they were introduced in '68.
Although, if it's a late '72 or a '73 340, he will also need to address the external balance issue when using the early trans., which is neutral balance.
