'90's LT1 short block under LT4 top end, using 1.6 rockers....what do you end up with?

I'd THINK damn close to an LT4. If you take an LT1 cam, add 1.6 rockers, you get essentially the same exact lift as the LT4 cam's lift specs.

Asking b/c my son found a super cheap, pretty clean, 70k mile '96 CE LT4 with a seized motor. I'm thinking that an LT1 shorblock would "fix the problem" and be a good flip.

 

Essentially the same, the heads and intake are the main ingredient. The Lt4 block is a 4 bolt whereas many other Lt1s were 2 bolt blocks.
I ran my 96 z28 for many years with just bolt-ons longtubes, 3" X pipe,1.6 roller rockers,52mm TB, M6, 4.10 gears and drag radials best pass at 3100' DA was a 12.98@107 on NX 150 shot 11:36 @ 117

 

Right on.

3100 DA in 'Vegas is pretty good...for Vegas. My track was at 4200'....our DA was almost always around 9000'. I ran at 'Vegas once w/my box stock '92 LT1, it was over 100*F and the DA was slightly over 6000'...still managed a 13.5x@105, which I was pretty happy with.

Your trap on the juice is moving.

 

What about fitting the crank sensor to the LT1? Use the LT4 timing cover, I assume?

 

yes, timing cover, reluctor ring and balancer

 

If using 96-97 PCM (or 0411!) or otherwise using a crank sensor, yes.

 

Super, thanks.

Yep. The idea I'm thinking of is to replace the bad part of the LT4 (the short block) with A GOOD LT1 .....short block. So all the LT1 "stuff" (heads/intake, sensors, injectors, etc) would come off the LT1 short block....then all of the LT4 "stuff", (heads/intake, sensors, injectors, etc) would bolt on to the LT1 short block and you'd (mostly) have an LT4...w/o "rolled fillets" on the crank. Or 4 bolts.

 

Sounds fun. I remember the parts counter had at one time sheets with crate engines. The 3400 for replacing the 2.8 TBI was on the same sheet as (IIRC) the 4bbl LT4 crate.