The way I always have timed 235's is to advance the distributor until it starts to run rough, then back it off until it smoothes out. Then drive it to see if it pings, if not you got it right if it pings, retard it a tiny bit at a time until it stops. May be "backyard shadetree mechanic" way, but it works. I had a 1953 Chev. sedan with a 235 that ran like a champ, held several drag strip records and got me trophies, that I timed like that and it did great.
