I think you should use the proper bent wrenches. Theres a forum member Doc (in Tucson) who made mine for me. Price was fair and they work great!

On the subject of "possible damage being done." Some incompetent dick somewhere ****ed the adjustment nut on my number 1 Exhaust and number 5 intake valves at some time in the past before I got the car. I ground a 14mm spanner to accept the odd shape of those nuts and bent it so it would fit.

One thing to note for your first valve adjustment that I don't think dieselgiant mentions.
If the huge (30mm I think) flat nut on the valve spring is turning when you're loosening the lock nut (bottom nut if you're doing it factory way) you're not actually accomplishing anything. You'll need to find a way to keep it from turning while you make your adjustments.