2500 HD frame & LQ4 swap into 78 K20

I picked up a wrecked 2002 2500HD 4x4 to use as a donor for my LQ4 / 4L80E / NP261 swap into my 1978 K20 truck.

I had planned to swap the drivetrain into my 78 and retrofit all the fuel system, convert/modify the driveshafts to work and do all the normal swap stuff to get the LQ4 into my 78. I had a different thought after reading a thread on a guy who swapped a complete corvette chassis & drivetrain into a Honda Civic that this could probably be done in the case of my truck but far easier. It might even be faster than the engine swap with the benefit of the newer chassis & brakes. I might even retrofit the 2002 dash and try to keep the air bags functional if possible.

Both my trucks are RCLB trucks so they should be similar in dimensions. Unfortunately they are both buried under more than five feet of snow that we have received in the past three weeks. I can not get out there and take some wheel base, track width & wheel position measurements on both rigs to compare them.

Has anybody done this swap before to put the 78 body onto the 2002 chassis?

Anybody have basic wheel base & track width information or a link to where I could find them?

I don't have any helpful info, but want to comend you on your attempt!

Thanks for the encouragement.

At the rate it is snowing it will probably be a couple months before I can even see the trucks again so it may take me a awhile to make any progress on this.

I did find that the 2000+ dash & steering column will not work in the 73-87 due to the cab depth being too little on the 73-87. There just is not enough room to spare between the steering wheel and the seat for anybody taller than 5'-0" to fit.

I am going to try to fit the gauge pod with drivers information center into the 78 dash though.

The 1973 - 1987 Chevrolet & GMC Pickups Message Board - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Might troll through here.

Sounds like a cool swap. Modern powertrains in old trucks is just way cool. :D

I have seen a 1972 K5 Blazer on a 1988-1998 short bed 4wd chassis before and it didn’t look quite right.

One issue you would have with the 2002 chassis under the 1978 body is the wheel base is longer on the newer trucks by close to 6”. That could easily be dealt with by cutting off the rivets on the rear axle spring hangers and sliding the axle forward to line up with the wheel well opening on the ’78 body and reworking the rear driveshaft. But the next issue is with the track width as the newer trucks have a much wider track width. It would look silly with the wheels sticking that far past the fenders and even worse if you run aftermarket wheels with a heavy offset. Plus you are into off-roading you would have a chassis with the less than sterling IFS front suspension.

Mounting and leveling the body on the 2002 chassis would be a challenge of its own as well the complexity of selling the truck with 2 titles if you ever decide to as many states get weird about matching body and chassis VIN’s. Potential buyers often get spooked about these type creations as well.

I would recommend just installing the powertrain into the ’78 and call it a day. As you probably already noticed, you won’t be able to use the 261 case with the ’78 front axle though as the transfercase front output shafts are on opposite sides. A 241 transfercase out of an late 80’s or early 90’s Blazer or Suburban should bolt right up to the 4L80E or you can get an adapter from Advance Adapter$ to bolt a NP205 to the back of a 4L80E. Or another option would be to convert the ‘78 over to a Ford Dana 44 or 60 with the left side pinion and keep the 261.

I recently swapping an 8.1L in a ’78 K10 as well but kept the original SM456 manual transmission and 205 transfercase. The 8.1L was a direct bolt in whereas the LS engines will be a tad different but easily achieved with engine mount adapters.

L18 8.1L - a set on Flickr

As SVIC said, the 67-72chevytrucks.com is a good resource as there a lot of people doing LS swaps into these old trucks.

I agree with the powertrain swap.

I had originally planned to do just the drivetrain swap but thought the frame swap could be possible. I have no problem fabricating body mounts & shortening the frame and modifying the driveshafts but the track width problem in the front with IFS is something I don't want to spend the money on to overcome.

I have bad knees so driving the K20 with the SM465 is painful for me at best so a 4L80E swap was part of the original plans. That is why I am not driving it right now.

I have been looking for a Ford Dana 60 front axle to swap into the truck to work with the 4L80E & NP261. This truck will be worked hard so the Dana 44 is one of the weak links needing to be upgraded. I may have to drive the truck around as a 4x2 until I can locate and rebuild a Ford Dana 60 to work with the 261.

I could try the 4L80E to NP205 conversion as well but I still want the Dana 60 front diff eventually. This would give me a functional 4x4 again right away though.

I have the whole donor truck so I am going to try to use as much of the 2500 HD parts as I can on the 78.

The frame swap seemed like a nice idea but the expense involved to correct the track width differences rules it out for me.

Thanks for the input everybody.