The 235 engines changed from 15 head bolts (as in 1952 and earlier 216/235 engines) to 18 head bolts (as in later 235/261 engines).

The information above pertains to 1953 216 engines (cars and trucks, I think);
and,
The information below pertains to both high-pressure and low pressure 1953 235 car/truck engines (I think).

In 1953, the 235 Powerglide-equipped car engine was a high-pressure engine; but,
the 1953 truck engine and the 1953 non-Powerglide car engine were low pressure engines.

Internal Lubrication of High-Pressure 235/261

lubrication of the rocker-arm & valve mechanism
from the 1954-57 Chevrolet Truck Shop Manuals