made my custom shift linkage....

In reversing the 2 forward levers, do you mean by placing the 1-2 gear operating lever in the 3-4 levers place and vise-versa?

I made the linkage all from scratch. I got some stainless heim joints from Fastenal, some stainless tubing, and welded some SS nuts on the the ends of the tube where I used shoulder bolts that hooks it up to the operating levers. On the shifter side, I had my buddy machine 3 stainless steel fine thread bolts down to the inside diameter of the tubing, slid them in and welded them up...

Yes. That's what I mean. That would allow you to straighten the shift rods completely up. Similar to the Hurst Super Shifter and Ram Rod linkage. Both their 1-2 and 3-4 rods were perfectly straight. That usually gives much more positive and smoother shifting. Also, that will "uncross" your 1-2 and 3-4 rods. That right there will probably help out a ton.