Front fork spacer length?

I plan on putting in a new pair of progressive front springs in my 82 XJ650. I have a front fairing on it, like a windjammer, except it a factory yamaha. I am also a big guy, 6 ft 280 lbs. The directions says to use a 1.5" spacer but I have searched this topic on the forum and found people using anything from a 1.5" to a 5" spacer. How do I determine how long the spacer should be? I have also heard that pvc is okay to use as a spacer. Is that true?

Thanks in advance,

 

1.5" is the length required for a 650 turbo. I just cut the stock spacer with a pipe cutter, it works fine. I cannot for the life of me figure out how you would stuff a 5" spacer in there. I took out the 1.5" and put in the slightly longer bit left from the stocker and it was a bit of a challenge to stick the spring back in.

 

I'm using bathroom drain pipe right now in my FZR. I do plan to update to aluminum next time I open them up (it was a royal pain to squeeze everything back in by myself).
As for spacer length, I had several folks suggest that I make a few spacers of different lengths and try them out one at a time. Another suggestion was to start out with the recommended length and shim it with additional washers until happiness was achieved.
All the advice I have for you bud.