What's in a factory K20 setup?

[backwoodsK20]

I just bought a '68 Chev 3/4 ton 4x4, it has an inline 6 (guy says it's a 292, could be a 250...), and a 4 speed. The rest of the truck is untouched, all stock. So, lets begin...
- What's the external difference between a 292 and 250?
- How is strong the transmission, compared to the SM465?
- How good is the transfer case? I assume it's a Rockwell from what I gathered.
- Did the diffs come with posi or a locker from the factory, and what gear ratio would they likely be?

I don't actually have the truck yet, I still need to pick it up, so I can't really go out and check for certain details right now.

[lowrollin70gmc]

1. The 194-250s have motor mounts symmetrical from each other, whereas the 292 has an offset passenger side mount, as well as being taller than the 250/below. Quickest way is to look at the passenger side and if the fuel pump in towards the front of the car compared to the motor mount it's a 250 and if the fuel pump is to the rear of the motor mount it's a 292.

2. No clue, but it's probably decent in terms of strength. Also, over the last 46 years it could have been changed many times over.

3. Again, no clue. I would guess parts availability is less than the NP205s.

4. There could be a factory posi in the rear and most were geared 4.10 or 4.56 (there's a chart somewhere on this site). Once again, the last 46 years could have had many of these parts changed out. Heck, mine was running a Ford D60 rear w/3.73s/posi that was nearly identical to the stock unit except for axle shaft spline count.

[special-K]

1. Answered

2. Plenty strong

3. Plenty strong. Only reason to swap is if parts are needed and you can't find them.If it ain't broke don't fix it. Just watch for leaks and keep filled with fluid.

4. Posi front and locker rear were options that would be listed on the SPID. The ratio should be 4.57:1

[Tx Firefighter]

#2- The SM465 is the standard for strength that other transmissions are measured by. GM never used a tougher trans. Even some dump trucks got the 465.

[Iron Hauler]

I think in 68 you may have an SM420 trans, I've seen both in the 68s

[backwoodsK20]

Originally Posted by Iron Hauler

I think in 68 you may have an SM420 trans, I've seen both in the 68s

I'll trust this thing is built like a tank and will take whatever I throw at it. I will run it hard, but not ruin it. One day this truck deserves a frame off resto.

[Iron Hauler]

Originally Posted by backwoodsK20

I'll trust this thing is built like a tank and will take whatever I throw at it. I will run it hard, but not ruin it. One day this truck deserves a frame off resto.

I'm sure it will do everything you want out of it, 4 speed 6 cylinder ain't much for the highway but is truly a work horse. Be sure and post some pics when you get it.