I am swapping a '99 454 into my '96 Sierra 1500 w/ an L31.
(Stock for now, hot roddin' will begin when the ol' budget opens up)
I have a complete, running '99 Sierra 3500 4x2 (OBS) as the donor truck. I have a few questions I'm hoping ya'll can answer

1. How do I know if it is an L29 or L21?

2. The donor truck has a 5spd, I'm going to be putting a 4L80E behind the 454 in my 1500. I know I'll have to shorten the driveshaft (going to put in a 1 pc shaft), move the crossmember, put a flexplate instead of flywheel, etc. But do I need to use a complete harness and PCM for an automatic? I have a complete harness with PCM for a Vortec 454 with a 4L80E (don't remember what year it came off of, I think it's '98, but I can recheck).

3. Do I have to use a '99 4L80E? If not, what other years will work with the '99 PCM? (if I can use it, 411 PCM in the near future, possibly be able to acquire before install)

4. I plan on putting my L31 back into the 3500 so I can resell it as a running truck, I'm pretty sure I'll have to change the pressure plate/clutch out for one for a 350, but do I need an adapter plate to bolt the 5spd trans to the block? What year/model should I get the plate and clutch for that will work with that trans?

5. Will my harness and PCM from my 1500 w/ auto work with the 5spd setup or do I need to find one for a manual?

I apologize for the lengthy questions, but I have searched around and can't find anything that answers any of them specifically. Thanks in advance for your input

 

Anybody?

 

Bump. Noone has any experience with this? I would just take it all apart and experiment, but the 1500 is my daily, so I would like to have everything ready to go before doing the swap

 

It's L29

Use 4L80 flywheel if you are going 4L80 route.

On the harness you have several options I'd send the harness to any of the sponsors on the right who build harness' and have them mod your OE harness for the big block and just flash your stock pcm with a 96 big block auto VIN and you are good to go.

If you have a full 98 harness use it. But you are going to have to replace the connectors where it ties into the dash harness on the passenger side behind the glovebox. Easy enough to do and make sure the 98 pcm is programmed for a big block and 4l80 and delete the antitheft so it will start and run.
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Put in a new gm fuel pump for safety sake unless youve done it recently. They are the same 4.3-7.4 and all engines in between.

Order a clutch and flywheel for 99 350 with a nv4500. 96-2000classic are all the same not one part different.

 

Thanks, I'll look into getting the harness done

 

Have them upgrade the harness to the 98 PCM the 96-97 computers are total ****.

 

I'm probably going to just do the 411

 

even better move

 

You might not like a one piece shaft on an extended cab unless you go for a nice custom one. Critical speed will be very low. My 76" factory tapered driveshaft went boom at about 5000 rpm in third gear (1:1 ratio).

 

It's my DD, not driven hard very often, she'll rarely see a hard 4K except for passing, let alone 5, but I will keep that in mind when I'm building the toy later. I only considered the one piece because I had heard horror stories of two pieces coming apart after 110MPH (I'm more of a highway runner than a red light racer)