Yeah i was looking at a set a 236's a guy was selling about a month ago, the chamber looks like a 781 casting so im assuming 118cc, i would assume the 236's are a small port version of the 781.
I know Mortec says they are 113cc but i'm pretty sure that's incorrect
If you don't like the 236's look for a set of 148's or 875's they were made into the late 80's and are easier to find.
They are the same as 241 castings and work very well on the 454
I just scored a set of 875's for a 402 that i have and im running a set of big valve 241's on a 454 that im real happy with.
Your 454 is probably a truck motor it would be interesting to see what casting number is at the back of the block, try and maneuver a camera back in there an snap a picture to find out what the number is.