Having trouble getting shifter to select low gear

I can't see how that homemade piece could move enough to cause your problem.
I did have the same problem with all OEM parts build ( column shift to floor shift change ). My shifter hit the console opening before getting low gear. I removed the console and still couldn't get low gear.
The factory service manual states to set up the shifter linkage adjust in neutral position. Do that and see if you get both park and low gear ends of travel. It worked for me.