Doug, I'd use 90 degree bulkhead fittings with bulkhead nuts and copper crush washers, Dowty Seals or Stat-O-Seals to prevent oil from seeping out around the fittings. I'd also use Loctite on the nuts to make sure they'll never come loose inside the pan. Why don't you want to weld on the pan? You'd never need to worry about the fittings loosening from vibration. Also, are you sure you need four drainback lines? Isn't one at the back of each head sufficient?
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