so i posted about 6 months ago with a build up thread on my ek which just started to run a few days ago. i swapped a k20z3. something i wouldn't recommend. but its possible. here are some issues that i had to deal with in doing the swap.

https://honda-tech.com/zerothread?id=1980301

tb- i converted the engine harness to 03 rsx type s. including the actual tb (i just got a bdl tb) and got all the sensors off a stock 03 rsx type s i am also using the original ek throttle cable with a bracket that was made to hold it to the tb. ill post pics soon.

Ecu- i bought k-pro for a rsx type s. and got the conversion harness from r*krew most of my stuff is from them cause i have a buddy that works there. along with the conversion harness comes a brown plug that took me a week to find out what it was for. turns out its just for a silinoid (sp) that should be it for ecu. once you convert the engine harness to 03 rsx its not that bad.

Speedo and shifter- these issues have not yet been figured out. im planning on using a s2k gauge cluster for the speedo but for now i dont have one. and the shifter is a tough one. so i tried to use the 06 shifter box but from the angle in needs to travel in the exhaust canal which doesn't work due to the heat might melt the cables together. so i ended up buying a Revo short shift box and rsx type s cables. and a heat shield i forget what brand it is. ill also find that out for you. so in using the rsx cables it messed the entire configuration of the shift pattern up. basically flipped upside down. 1st is where 2nd is and 2nd is where 1st is and 3rd is where 4th is... and so on. reverse is all the way over to the right and up. its goofy ive gotten use to it already and i have only have had the car going on my third day. but its annoying. ill try to find a solution. it only does it cause the 06 box does the opposite. it pushes instead of pulls the cables which connect to the tranny.

more issues...
axles- i came across an issue with the axles idk if i got a bad set or something but i bought some r*crew axles and it didn't work out. they were about a inch short on both sides. and your intermediate shaft is different so don't mess that up... haha when the r*crew axles were installed they got jammed so when i attempted to remove them i had to buy a whole new intermediate shaft which wasn't cheap because they the dealership told me that they are "discontinuing" the production of that part because its being revised" idk some bullshit along those lines. so i bought hasport axles and they fit fine.

oil pan- the 06 uses a completely different oil pick up so the oil pan sits about an 1 1/2 inches to 2 inches off the ground. which for me is a little nerve racking. again i haven't figured anything out. really the only thing you can do is buy a whole oil system from a rsx type s and install it and use a ep3 or k24 pan cause the pick up on the 06 wont fit any of those. another option is dry sump kits. basically eliminates the pan. which i am saving up for now. ends up costing about 3k.

off the top of my head that should be all the issues.

honestly i would have done it differently. i would have used a rsx type s. this engine is a huge bitch. idk if its worth having the low mileage but i cant really talk cause my motor runs great if you decide to do the swap ill be more than willing to help. id hate for anyone to go through all the **** i went through. took me almost 9 months and just over 10k from start to finish. it was not fun. haha

if anyone else has done this swap id like to talk with you.