It's easy to lengthen a front one, but it will only have a longer tube, and not added slip, so if you have any axle wrap at all, you may pull the shaft apart, but i don't know much about allpro's....i run rears up front, and couldn't lengthen a shaft without it slipping apart.
I made a square tube with over 8" of allowed pull and about 3" compression and i got enough axle wrap once to pull it apart. It works excelllent though....here's a writeup from when i made it awhile ago.
http://infohost.nmt.edu/~jscarbro/driveshaft.htmIf you know exactly what lengths you want, i could probabaly make you one (square or just lengthened tube)
Let me know.