Definitely test the .039 HSAB's but don't sweat changing from the 64 to 65 jets (just yet).
ONE CHANGE AT A TIME!

Note: I don't think that they would be too lean in your case. I swap back and fourth from .036 to .039's on my secondaries as the outside temps change to tune my WOT A/F readings.

McMasterCarr.com is your friend. They have drill bits in all of the small sizes that you will need. I bought a dozen or so from them so that I could drill out my IFR's/IAB's/ and MAB's.
http://www.mcmaster.com/#standard-drill-bits/=t0eh03