Id think it would be D A N G E R O U S to fit a D7 Contra to a ABC Liner !
Some pylon types expand the bore with Nitro & RPM or whatever . And have to de expand / shrink back to normal . AS YOU KNOW .
The correct type ' DIESEL " head for the ABC would likely be like a ROSSI , or THIS ,
Where the HEAD goes done right the way , shimmed . With the CONTRA in the HEAD . So the bores un stressed there !
As the D& Contras real short , it could derange the chrome even , and stretch the brass liner . DO NOT DO IT .
Likely a Rossi head would bolt on , if you hve one .