I'm not maintaining the Slackware version for pkgsrc anymore nor its pkgsrc bulks.
Hint : install a minimal Slackware (A, AP, D, K, N sets), get pkgsrc and bootstrap it (cd bootstrap/; make install).
I suggest you make your own prefered package respository with "make package" instead of making bulks.

Here's a nice pkgsrc guide
And here are lots of other technical notes

-Pierre-Philipp