I have a 1970 mach 1, 351 cleveland engine 2 barrel and a C6 tranny.I would like put some headers in it, no one seems to know so far what my choice should be.
different people say the headers are gonna hit the tranny.
please help    

Might try FPA (253) 848-9503

Expect to pay well for them.

These Walker 85063 at Summit might fit - notes say no, have seen where others have used with an FMX and AOD.  Cheap enough to cut up if needed.  

We run Tubular Automotive headers on the 70 here with a 351C 2V, but that motor has a C4 behind it.

You can also ask over on 351 Cleveland.net