new BBEdit window with selection

Am trying to do the following:

I have a file with 20,000+ lines that needs to be broken up into individual files containing 500 lines each. Need to do this every month or so from updated master file.

The script that I writing only selects one line, not the sequence of 500 I need.
tell application “BBEdit 6.1 for OS X”
select display_line 1 of text window 1
select display_line 500 of text window 1
make new text window with properties {contents:selection}
save text window 1 to file “Larkin:Users:da:Sites:01.txt”
end tell

To get a chunk of text selected, this works in BBEdit 7:

tell application “BBEdit”
select lines 20 thru 50 of window 1
end tell

I don’t think the “display line” command will accept a “thru”. It is used when the text is soft wrapped in the window but the real “line” ends with a hard return. In those cases, I prevent BBEdit from soft wrapping (so the lines go off the page).

just what I was looking for