if you need a new head anyway, pull the old one and measure the bore - 3-9/16 = 235 and 3-3/4 = 261
also I've been told the threaded oil pressure sending hole in the drivers side of the block is 1/2" on 261, but smaller [3/8?] on the 235

Bill

Moved over to the Passing Lane

"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir
"When we tug a single thing on an old truck, we find it falls off" ~ me
Some TF series details & TF heater pics