Very easy to do...I do it on all the ones I buy or build myself... If you have a lathe you can make a bushing for the bottom,, Then all you need is a slip collar with a set screw... Cut the one you have long,, Then figure where you need to stop the outter part of the column,Take your time in cut it as straite as you can. Then either get a bearing or make a bushing for the bottom.. Once you have it in place,just ping three sides with a center punch...
The collar will be on the end to stop the shaft from coming up..It can't come down..Theres a nut at the top stopping that from happening..Inside at the bottom where it goes through the firewall weld a 1'' peice of flat bar against the fire wall (not to the firewall, to the column ) with a 1/4'' hole in it so once it's welded to the column you can bolt the bottom of the column to the firewall.. Very easy to do..
You don't even need to take the column apart to do this..
When I do a custom build and don't make it myself, I order the longest flamingriver I can buy, Then once I set it in the car I can shorten it to the size to better fit the car I'm building..