My suggestion would be to first look at what is causing the problem. There are some wear points that can be repaired and bushings that can be replaced. Check to see if there is grease in the shifter control box and adjust the linkage.
I believe there are still some aftermarket 3 speed floor shift conversions available. Also some used units providing the're not worn out.
You could just be replacing one problem with another one.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine