no, not necessary - I've put about 40,000mi on a 57 235 w/ unleaded, no probs, and have run lots of old 283's, 327's w/ unleaded - story is the valve seats may wear a bit faster being not-hardened, but nobody seems to think it really affects longevity - when ya get yer motor rebuilt, ask for hardened seats
and welcome to the garage, where yer every puzzle can be solved eventually!! grin

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 & Rust-a-holics Unanimous parking lot