Your block is interesting. All the normal casting features indicate it is a 39-40 "99" block type (239 cubic inch engine):
- Round center water hole
- Upside down trapezoid lower water hole
- Core plugs in the oil pan rail
- Flat intake gasket surface
In the engine block identification thread we have pictures of a C69 block, which has most of the features of the USA 59 blocks. We might need to add a C59 block category to the list. Please keep posting pictures!