I use regular open-ended wrenches. I always have room to swing them between the tubes. Perhaps I just got lucky. One is a Craftsman box and the other a HF set of thin open-ended wrenches. I recall you need 14 mm, and I found 9/16" also fits for a 2nd one for those w/ old U.S. cars like me.

BTW, as you do the final tightening, the gap sometimes changes. Takes practice to push more on one wrench than the other to hold it, since the valve can spin. I usually re-learn on the first few valves, then goes quicker.

But, if you want to bend wrenches I found you can pickup loose wrenches at swap meets for $0.25 ea. I grabbed enough to make sets for my sons. Many are better U.S. made steel. I keep extras to choose, because sometimes you need just the right handle length, offset, or hex clocking for that fussy bolt, especially on newer cars where there is little room.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans