Shouldn’t be too hard to find a NV3500 from a 97-07 2wd Silverado
I recently swapped in a 3500 to replace the SM465 four speed
Mine was 4wd so harder to find
And Chevy didn’t put the 3500 behind the 5.3 only behind the 4.8 but it’s held up fine behind a 5.3 with 35” tires and a teenage boy driving it
And it’s a blast to bang thru the gears
We ran it with the old 350 for a while then swapped in an LS 5.3
Think we used the existing crossmsmber and mount from the four speed
Your biggest job is going to be the hydraulic clutch
I used a stock square body mc and used all thread to mount it to the firewall so I had some adjustment and I just drilled a hole in the clutch pedal and bolted the mc rod to the pedal
I bought a new slave throw out and had a local hydraulics shop make the hose
They cut off the weird connector on the slave and welded on a threaded connector they had in stock and made a flex hose to run to the mc
If your clutch pedal pivot up top is worn out behind a bushing repair
I discovered that the brake pedal from an automatic will work if you cut off the bottom of the pedal and discard it and flip
Over the top half
Then bolt the bottom half of your old clutch pedal to the flipped over top half of the automatic brake pedal
Also when you are mounting the mc
Cut the large hole first and get it where you want it and then use the mc mounting holes as a guide for drilling the bolt holes in the firewall
Don’t try to drill all three holes at once