the following must be true...................it's from the internet
late model 12.7:1 quick ratio gearbox
ID markings YA ,WS and HX
Line Thread Size : M18x1.5 and M16x1.5
Number of Mounting Holes : 3 ( missing leg H-pattern )
Input Shaft Diameter : 3/4-inch
Output Shaft Diameter : 1 1/4-inch
Number of Turns Lock to Lock :2 1/2 - 3
1984-88 Monte Carlo/Malibu with Z65 suspension
1983-88 Malibu,El Camino
1982-92 Camaro except FE1 soft ride suspension
1984-87 Regal withFE2 or FE3 sport suspension
1983-84 Hurst Olds
1985-87 Cutlass with 5.0 ( VIN code 9 )
1982-85 Trans Am
1986-92 Firebird except FE1 suspension
1986-87 Grand Prix with FE2 touring or F41 heavy duty suspension
or go to Rockauto and search under T-TYPE / Grand National
click & buy
The thing about buying a box these days,where they're rem'd and not new there's a chance you're getting stuck with a standard ratio box that was once a core.
I bought my box from gm way back,I'll l see if i still have the slip for it tonight
There was also an article in Hot Rod some years ago. They mentioned using a steering box from a Jeep Grand Cherokee. I'll see if I can refer back to that article for more info. Either way, you'll still need to replace that pitman arm.
If I recall, it's also a quick ratio box.
I found it. They mention using the '96-'98 Jeep Grand Cherokee box. It has the 12.7:1 ratio and is the 800 series box.
So, I'm thinking that it may be easier to source one of these from the junkyard than one from a Monte SS. GN, TA, T-Type, 442, H/O. Z-28, etc. Plus it's probably a newer box with "hopefully" less wear and tear on it....but that's a crapshoot.