Well, even in stock form, valve lift will be close to .400 from the seat, and even the deepest pistons sit at around 1/4 the height of this. Even at an angle, those valves will be pushed far past where the the piston top comes up to, and even if it clears the dish, would hit the sides of the piston top. This is assuming the valves are open fully and the engine made a full revolution. This would be exacerbated by anything over stock cam specs and deck/head milling. Short answer: yes, it is an interference engine.
Interesting, I never considered this (although I have a 340). I spun my timing chain earlier this year, but just enough to bring the compression down to 30psi. Guess I got lucky. I did not have far to go to re-align the timing marks with the new gear. Maybe that's why they use a nylon gear?
A compression test should be way higher than 30. You've got bent valves if it's 30. You should be over 100. Do a leakdown test. I bet you'll find your valves are leaking. All your cylinders should read within about 10% of the highest reading. They used a nylon gear because they run quiet.
When it skipped timing, the compression was down to 30. Once I put a new gear in and reset the timing it was back up to 155. The compression test with 30 in all showed why my car wouldn't start and let me know it was the timing.
Many thanks to all for these replies. My timing chain went being the reason for my question, and I have two cylinders (1 and 8) compressing at half of what they should.