I don't know what the numbers mean exactly (most likely plate current draw at a particular bias voltage and plate voltage, although by itself it means nothing because it might not be the same as what your amp uses) but two tubes marked 38 and 39 will be close enough to use together *whatever* the measurement means - that's well within 5%, which is what would normally be considered a reasonable match.
If you're going to use the broken tube, you can - just be *certain* to check that the tube filament has lit up *before* flipping the standby to play. Very important - if not, you could blow the tube or damage the amp.
It's always good practice to do this anyway. Just the other day I blew a (luckily old, using it for testing, but still annoying) Sovtek 5881 because the amp didn't have a standby switch and I had it in the socket one notch out of the right position - and that was *with* the locator pin still there. Sometimes they will go in if the socket is a bit oversized or the pin a bit undersized. I should have been more careful...
