Engine number 12539256 belongs to an improved Model T?
This would be the block for a 1926 Model T, so the answer is yes. This block was produced at the Rouge foundry.
Thank you, Royce. So, my 25 no improved got a 26 engine somewhere in time.
The Model Year changed to 1926 on August 1, 1925.
Your 1926 engine could be original and correct, although the vehicle was produced in 1925.
The body and fenders should tell you for sure what year your car really is.
Your engine was built Oct. 21, 1925 and is a 1926 model engine.
Model year actually changed to 1926 on August 3, 1925. There are only two days at the end of July, 1925 that an improved engine COULD have been used in a 25. Those are engines 12218729 through 12222528 so Rodrigo's engine is not correct for a 25 or before model.
Also, The engines were being built ahead of time since they were installed in a ready chassis. Although the 1925 engines stopped being built on July 28, they were most likely installed in 1925 chassis through July 29th while the 26 engines were being assembled for stock. The factory was closed until August 3rd when the improved car production started so it's highly unlikely that any 1926 style engines were installed in a 1925. If they had been, the engine would have to fall in the range mentioned above.