Exactly the same, all the hardware from one, fits the other.
The AVT-40, or select fire version of the SVT-40, was thicker in the wrist area to withstand the pounding from full auto fire. Easy to identify, the AVT stock has two safety cutouts, the one on the right will sometimes be plugged with an arsenal repair.
All SVT's that were re-arsenaled, were fitted with an AVT stock. All AVT's were converted back to SVT's then, because they couldn't withstand the pounding any better than the stocks could.
Good luck finding one, your only chance is maybe Marstar in Canada. There's a forum member on Surplus Rifle Forums that is making duplicates of military rifle stocks for the members there at a reasonable price. The catch is, he needs a stock for a template. I know he has had several requests to make replacement stocks for SVT-40's.
This is mine with the Naval Infantry version of the AVT stock, and the dust cover scope mount I fabricated. You can see the stock repair above the trigger.