Lt1 to Ls1
The LS1 will fit, but you need to bring it over with the K-Member from the newer car. You will also have to use a hybrid LT1/LS1 CAI to get good airflow into the LS1. The LS1's induction setup will not fit under the LT1 hood. (You could get a cowl-type or Ultra-Z hood and it might work--not sure.) Of course, you'll need the LS1's PCM etc... There are likely a number of electrical issues--especially related to the instrument panel, but since this mod has been done before, there are known solutions out there--I'm not sure of them though. These are just some things to think about. (The '97 is the best LT1 to do this mod to because it has the 98+ interior.)
The LS1 will leave you with a bit more room to work under the hood--it's laid out a bit nicer than the LT1. The trade-offs, in addition to the ones listed above, are that LS1 mods are generally more expensive than the equivalent LT1 mods, but you often get a little more HP out of them. To me, one big factor is the block being 100lbs less. That's like adding 15hp right there!!
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basically just find a wrecked LS1 and start swappin' it all over, may have to repin a few things but i dunno.
if you wanna keep the LT1 hood/bumper cover you'd probably wanna get a cowl or ultra-z hood.
I thought about doing the same thing, but for the price (and that you already have a 4340'ed r.assy) you may as well just load a 12+psi s/c onto the 383 and start smokin' LS1's. with some hogged out heads on 8-9:1 compression you'd be hard pressed to find ANY LS1 that could beat you. With the exception of people who have high five-figure budgets of course.
edit: oh yea, and for LS1 conversion you'd need to either convert the fuel system to dead-end style or find a 98-style fuel system (i think that one had the return system).
I second the other comments on how your money might be better spent. The LT1 can kick some serious but with a few $$ into it.

A note on those AFRs; They are expensive and there is a LONG wait for them. I ordered some back in July and did not get them until late November. Ended up selling them because the cost to have them ported was outrageous!
Pillagenburn has it right with everything that needs to be swapped. Its not a simple job.


