Your engine if original should be the 261, not the 235. Add pictures of the casting number and stamped engine code found on the passenger side of the block and see if it has "Captain Bars" back by the starter confirming it's a 261.
Mike B
Picture of captain bars on '59 261 and Firestone RH-5 (aka widow maker) wheel
BC 1960 Chevy C10 driver 261 T5 4.10 dana 44 power loc 1949 GMC 250 project in waiting 1960 C60 pasture art Retired GM dealer tech. 1980 - 2022
