August of 53 would put it in the realm of 54 model year (August retooling) which is first year for 261. 53 powerglide Head, i don’t think any damage. Frankly, the block is what you want if it’s a 261. The 54 blocks are the stouter of the 261 blocks in that the cylinders are thicker and can be bored larger, read that, good for rebuilding. Will wait to see the casting number and a photo.
