Gdads51,
Thank you for the additional information.
I took the photos of yesterday morning before my drive back to KC and did not take the valve cover off, I will do that next time to verify the #s.
In the photo I attached showing the block numbers 3733813. The fourth number apears to match a 3 more than an 8. which from the numbers I found indicated a 1956 261.
Is it possible they used a 1956 mold to cast the block in 1958?
Though it could be a red haring, the oil fill hole in the valve cover is in the front of the cover like those from 55-57.
