An auto car on a tow dolly?

I used a tow dolly with my 68 cuda 904 from springfield oregon to bellingham washington without unhooking the driveline. Thing is that I started the car and let it idle in neutral while under tow. Was it the right thing to do...maybe not but that was 6 years ago and am still running the same transmission today. Worked fine with my built 318. now that it's behind a 408 I am seeing slippage at the 1-2 shift but I don't think that's because of the way I towed it...