These numbers check out; check math and try this at small scale initially to be sure it works!

for 1L 0.8M K PIPES, pH 6.5

241.896 g/L PIPES free acid

600 mL diH2O, 2.9 pH initial

stir and slowly add

112 mL 10M KOH

PIPES will not dissolve fully until pH -> 6.5

add diH2O to final 1L volume

Thank you Edward :)