I've never walked the Green course at Bethpage so pardon me for asking, but why does it "need lengthening"? Certainly at a five-course complex there is room for one course that isn't 6900 yards, isn't there?
Tom, as someone who has played the Green many, many times, there actually isn't anywhere to go to lengthen in so it's a moot point. Here's the hole by hole summary:
#1: Tee box is just to the right of the Black's, same downhill kind of shot but shorter
#2: Across the road, nowhere to go back to lengthen
#3: Uphill, blind par 3, ditto
#4: Fun downhill par 4, again, nowhere to go back to lengthen
#5: Dogleg left par 4, tee can't be moved back (maybe 10 yards tops)
#6: Par 3, tee can't go backwards
#7: Par 5: trees behind tee box, can't be lengthened without major work
#8: Tee is just behind #7 green, nowhere to go
#9: Outstanding par 5, green complex reminds you of #1 at Spyglass but again, nowhere to go to lengthen
#10: Very short par 4 from elevated tee but nowhere to lengthen it
#11: Par 3, tee is adjacent to #10 green
#12: Short par 4, fun hole, can't be lengthened
#13: Par 4, ditto
#14: Par 4, ditto
#15: Par 3 from elevated tee, can't be lengthened
#16: Par 4, ditto
#17: Excellent par 4, over 400 yards, ditto
#18: Excellent finishing hole but it's against Round Swamp Road (tee is very close to #1 green, which is very close to Black #1 green) and is as long as it can be.
The Green is a good, fun course to play but not an enormous test for someone with length, it would be a pitching wedge to most of the holes for them.