i'm not sure about a 235 but for 250/ 292's i have used brake line to make a tube. i don't remember the actual size but i bought it where the od is slightly oversized and cut it down to a shoulder about a inch down on my lathe. then drove it in. you can even use the original mark on the dip stick if you made the tube long enough and put it in and measure down to freshly filled crankcase. then cut off with a tubing cutter or you can rescore the stick. can rebend tubing to close to original bends aswell. i'm sure they turn up on ebay from time to time. hr