Rear wheels under power in Neutral 727 trans.

Changed a leaky trans gasket on my 69 GTX.Now the rear wheels are engaged in neutral.All linkage looks fine you can feel it move from gear to gear.Its fine in park.I didn't touch anything else.Any ideas?
Thanks

"somehow" you bumped the shifter linkage out of adjustment.... if the wheels are moving, it's not in neutral. Will the wheels stop turning if you put the shifter between gears....a little more forward or a little more back?

Did it do this before? Or did you never notice it before?
A tight clutch pack in the trans will cause the tires to turn in neutral. It won't move like it's in first gear or anything, but it will move slightly. If the car is on jackstands, the wheels can move enough for you to think it's in gear.

Yep , at least one of my cars does this when in neutral on jackstands. Turns at a pretty good speed too.

Same here. When its on the ground, it doesn't move.

Fluid flow friction causing it. Setting it back on the ground will stop it.

How are you determining the wheels are engaged in neutral?

Does it take off down the road ?

I put it down & it appears to be fine.It was up on jackstands but it was definitely moving under power I tried to stop the tires with a long 2x4 & couldn't.

If you put it down on the ground and it's not moving then you didn't try hard enough or your engine is idling at too high an RPM. I have stopped the tires from moving with my foot against the side of the tire.

The tires are moving because of parasitic drag of the fluid between the clutches and steels, the fact that it doesn't drive away when you put it on the ground tells you it's a non issue ... unless you try to make it an issue and injure yourself ...