Few things I found doing my LS Swap
 

I have a 1969 C10 that I built from the ground up, and in doing so i decided to do an LS Swap. I bought what was to be a 2000 5.3 and discovered it was a 2000 4.8. So, after a Crank and rod change out, I got a 5.3, bored .60 over, rebuilt stock heads, "Hot Cam", all new sensors, headers, PSI wiring harness and computer, "Corvette style" fuel pump, filter and regulator, stayed iwth Multi-Port fuel injection, rebuilt 4L60E tranny, converted to Hydro-Boost brakes with all WilWood stock sytle upgrade replacement disc front and rear, 3:42 posi rear gears.
So with all that said, i started with a Holley Sheet Metal (Sniper) Multi-Port intake and 92mm throttle body, rebuilt 24lb injectors. This intake would make a sound that resembles a bearing going out in the alternator. It was unreal. If you place your hand on top of the intake it would go away. The throttle was responsive, but not like it should be. The sound was a Harmonic resonance that i just could not stand, either could my tuner. So, I decided to change out to a Holley open style plenum with a 4150 mount (where the throttle body that looks like a carb could sit) but till be Multi-port. I also changed out the stock 24lb injectors for new Accel 36lb injectors that required conversion wires from the stock Mulitec injectors to EV1 injectors, and DAMN did that thing wake up! It is incredible. My personal belief is that injectors are main influence on waking the motor up.
So what i learned is this, The injector size is very important, so do not skimp (as i did) if you do ANY modifications to the engine. There are calculators out there that will help with what size to run. Also, i took the conversion wires and made them longer by 12" with solder, heat shrink and same size wire for the the injectors so that i could route the wires under the intake to clean up the look, with no issues to date.
My experience is that the swap i did was not cheap honestly, but for the run ability of the motor with Multi-Port Fuel Injection, so worth it. If you are considering the LS Swap, do the research, figure out your direction with what you want and budget must be considered because you can go from not much to oh you must be kidding me very quickly.
Hope this may help.

Re: Few things I found doing my LS Swap
 

That is good info. My sister's husband who thinks I am crazy for being a NA guy has run into that a few times with hopped up Jdm children's toys. Where a manifold for whatever reason will not work right on a certain engine. I typically run ported dual planes, and never felt that to be a issue. Even when my experimental builds ran perfectly fine, and didn't do much better with the several manifolds I tried.

Isn't there a thing where you want to run your injectors at 75% duty cycle or so to avoid issues.

On my LT1 350 I thought about going with upgraded 01+ vortec fuel injection, but it was not a well charted course. So after my tunnel ram build I want a supercharged new 4.3

Re: Few things I found doing my LS Swap
 

Good info. I know there are a couple of grades of intakes, too... one a little thicker for boost that is stiffer to mitigate oil canning under boost, and may be quieter.

Good note on the injectors too - unfortunately the non-flex fuel injectors are pretty weak. The flex fuel ones are 30+ lbs and generally good for moderate build (400ish wheel hp.)

75% is a pretty conservatively safe number. In my old import days we ran some up in the 90's but it wasn't great practice. Liked to keep them at or below 80%.

Re: Few things I found doing my LS Swap
 

I believe that most will be closer to 80% duty Cycle. I was running on a very tight budget and with that said, i tried to cut a fast one and stick with the cheaper stock versions. It is my belief and experience that this is wrong, that if you do ANY upgrades you really need to run bigger injectors. Now that I am, it is so much better. The intake thing was the craziest thing I have ever seen. I never ever thought that this would be an issue or could be, but evidently i am not the only person to see this. The new intake is great so far.

Re: Few things I found doing my LS Swap
 

I had no idea that there are different grades of intakes, but I will say that I can see why there is and if you ask me they should get rid of the version I had because I searched and found others that have had the same issue. So you would think that they (Holley) would address it but I have been in contact with them and they seem to want to be believe it is just mine and will replace it for exactly the same one. This honestly did and does not make me happy for the response, but I was not surprised.
I got the new intake and it works great so far and i feel that it pushed me to change out the injectors and that has been awesome.