Not exactly the same, the crank balancing is different between the two, 305's also had cast internals, and 2 bolt mains.
Not sure why the push for SAE30? This isn't 1983. Back in '05, I scored about 40 gallons of Delo 400 SAE30 from AZ for $.99/gal. It was a good deal and discussion back then revealed it behaved more like a 15W30 than straight weight. Still, not sure why you would not run a quality 5W30 lube in this stock 305. No extra ZDDP is going to save a physically inferior junk cam. As far as flat tappets go, there are millions of GM small blocks (and Jeep 4.0L/2.5L) engines running around on modern oil. I just don't see the value in running $12/qt oil in a 305.
Production engines of that era both had forged rods. 305 Rods were lighter (we have used them in 350 Claimer Motors for performance increase). Both had cast pistons and cranks. 2 Bolt Mains were common on Half-Ton 350's.
Many people have a low opinion of the 305 even in 4BBL form because of the heavy vehicles they tended to come in and rose colored glasses when it comes to older cars. They remember the old 283 and 289 fondly without considering unless they were solid cam engines they only made about 140 bhp net and came in cars as light as 2600 lb. It's not really fair to compare it to a 305 that is stuck in a 2,000 lb heavier truck or Caprice.
Even the 8.5:1 LG4 (150 bhp) runs better than the typical 283 in the same weight car. A 220 bhp TPI would give a 283/315 Fuelly a run for it's money in the same weight car.