Wheelbuilding / Wheel Building / Wheel build help

I was hoping to replace open pro with excursions on a fixed wheelset (so i can rebuild the open pro to 105) with but the maths I did using values on spocalc gave me a 2mm diff in spoke length based on the different ERD.

Do you reckon this is a small enough difference to ignore?

I will recheck the numbers as was yesterday on computer, am typing this on phone.

I have always used the same spoke lengths for the Ambrosio series (Excellence, Evolution, Excursion) and Open PRO. Typically for a 32 3 cross with a standard hub (like your 105) you are looking at 295 front; 292/294 rear. If your OP was built with the correct lengths, it should be straightforward.