I think WPPSI goes to 7:2, but in any case, it is the WISC you'd need.
Before I read the rest, the low block design caught my eye right away. My dd took it at 4:6 and blocks was also her low score. Testers usually start with blocks, so maybe your ds was just warming up. That might have been the case with our dd, we really don't know.
As to how much it affects, you can perhaps sort it out since he was given the full test. You could substitute for picture completion. That would make his total scaled score for Performance 47. 47 is the total of the verbal IQ, so perhaps his performance would have also been 135, I am not sure if they do correspond like that.
For my dd, substituting the 9 she got for the 13 (4 points change) which is more in line with the rest of her non-verbal subtests, changes her Performance from 116 to 125. Her full scale jumps from 132 (98%) to 136 (99%).
Neither the tester nor us can guess what the better estimate is. I tend to think that the 9 is too low for what I see her do; but other times I am not so sure.
The 98% in the standardized tests would probably align with the IQ scores, especially with the substitution (my best guess). In that case, I see no real reason to retest. However, consider Cathy's points above.
One last thing, did the tester say anything about it? I find it interesting that he took only the 3 core verbal tests, but tester added an optional performance test. Optional subtests are usually listed between parenthesis to indicate that they are not used for score calculations.
