Here we have a TDC finder with clock (DTI) gauge, the one shown is for 10mm x 1mm threads, it also comes in 14mm x 1.25mm size.

DB2 to 2/4 MkII & all Alperform alloy heads + DB 4GT heads use the 10mm x 1mm,

DB MkIII & all DB4, 5, 6, S6, AM V8 (2 valve), DB7 i6 use 14mm x 1.25mm.

This is the item we use when not on site, nice bit of kit if bought with both types of thread & one DTI gauge it can be used on any post war Aston.

Or you could just buy the tool & source the DTI / clock gauge yourself

Comes with instructions for all known AML post war types

Shown is our workshop one, production ones will be similar 

Allow 10 working days for delivery

TBC