Speedo gear with TH 350 help

[62lwbc10]

Hey guys I just had my late 70's TH 350 completely rebuilt by an old school builder and it is performing unbelievable well. I have a brand new speedo cable and brand new speedo itself/ The guy did the "best he could" with getting the right speedo gear, but Im still reading a good 20 MPH over my actual speed. I have a SBC Chevy (305) for a motor. Can someone who is running a similar setup please let me know what type of speedo gear you are using? Number of teeth? COlor? Any info would be most helpful. Im sure I have a stock rear as, with the TH 350, the motor is revving a high RPM on the highway at 60 MPH (when the speedo tells me Im doing 80!).

Thanks all,
Mark