Working on trying to do the astro van shaft modification. I am wondering how much I need to extend the shaft, and what different methods have been tried?

I read one post where there is a "double d tube" that is made. I can cant seem to find that on the net(i suck at searching though). Anyone else found some?

I can not afford the flaming river make your own. Plus Ive had this shaft for about 3 years now.