[Test-Equipment] Anyone with a precision C meter?

[Barry]

I'm building a replacement for a failed standard capacitor in a General Radio GR-1617A.  I would like to get it as close 
to 0.5uF as feasibly possible.  It is comprised of several polystyrene capacitors in parallel that are slightly less 
than 0.5uF total.  I have what I think is an appropriate set of caps to fill in the last bit of C but I don't have a 
very accurate way of testing the existing C.

Is there anyone with a C meter that can measure this very accurately for me?  I would like to know within 250pF but 
something less than +/- 1nF would be better than I can measure it.

I have a 0.5uF 0.05% standard and I can perform an A/B comparison and that gets me pretty close, but I think it can't 
detect much more than a few percentage points difference and I would like to have it closer than that if possible.

I live in Northern Alabama and if anyone is close to this area it would be ideal as I could possibly bring it to you; 
however, I can ship it (and pay the return postage of course) if no one is nearby.

Thanks,
Barry - N4BUQ