Can the absorbance for the GOPOD assay (R-GLC4 / K-GLUC) be measured at alternative wavelengths if 510 nm is not available?

Yes. The most important thing is that all solutions including the glucose standard control must be read at the same wavelength.If the absorbance readings for 100 micrograms of glucose is between 0.9–1.0, then the results should be fine. 

Product Page (R-GLC4)

Product Page (K-GLUC)