Engine swap on 98 eclipse how can I tell if I have conpatable eng

If you pull coil wire from center of distributor cap, hold it close to metal part of engine. Have helper crank it, do you see/hear a spark jump? If so, the problem is in distributor. Make sure the rotor turns when you crank it.
Are you missing anything else? Engine cranking, do you have fuel injector pulse? If your missing both spark and fuel injector pulse, I'd have to check for rpm signal, comes from crank sensor.
I can only help with testing. You have to do the testing.

Call a auto locksmith or have it removed to a dealer i thnk this is a immobilisor problem her the ECU is not communicating with engine and its possible it may need re-programming as the bits are not talking to one and other to put it in a easy to understand way .

I would replace no 4 injector or at least swap it to another position to see if it is the injector or the wiring to the injector.

Have you checked the Cam sensor? The Cam sensor controls the injector pulse.

motor swap from v-8 to v-6. Injectors aren't firing

first need to check if fireing or not , your saying it seems to be? Try removing plug wire with engine running and hols a inch or two away and see if you here the engine idles down , if so it's fireing if not may be coil weak, good luck.

We check injectors with a needle stethoscope to locate the bad one. After we use injectors check lamp, (it is not costly and you can buy on line). If the light pulse, we replace the injector. If not then is an electrical problem. If you will replace the injectors please, buy original one from Cadillac Dealer, they are expensive. I bought aftermarket for north star engine, they were bad, and I bought again the original one. No more problems with injectors. Mine is a Cadillac Seville SLS. Hope will help.

I'm thinking the crank angle sensor is going out. I'd bet when you get no injector pulse, you loose fire too. that would tell me your crank angle sensor is gone.

I assume this 'complete' tune up was plugs, wires and plennum (intake surge tank) gasket?
If so, recommend you first check to see if you are getting an injector pulse to the #3 injector (a noid light is normally used to verify the injector is receiving the 'pulse' from the ECM. The noid light is a very useful tool in finding out if you have problems with your fuel injector. It is cheap (around 10 dollars per piece), easy to use (if the light blinks, your injector is receiving the electrical pulse to open). If after you verify the injector pulse is present, the next step is to determine if the injector or cylinder is the problem. A simple verification process requires swapping the #3 injector with another to see if the misfire moves to the swapped cylinder.(.i.e, move #3 injector to #2 cylinder & the #2 injector to #3 cylinder.).. Then run engine to see if the P0303 changes to P0302. This would VERIFY the injector is in some way defective. If the misfire STAYS at #3 cylinder, you'll want to perform a compression test of all the cylinders. If after this test you find #3 cylinder is more than 10% lower than all the other cylinders, do a 'Leak-Down' test to determine if the low compression is due to leaky valves (intake or exhaust) or whether the piston/rings are the problem. NOTE: If all the cylinders are withing 10% of each other during the compression test, the possible causes are, injector O-ring leak, vacuum leak at the intake manifold at #3 cylinder, or the spark plug not firing under compression.

check the injectors on that bank for pulses.. a regular 12v text light will do it should flash when cranking... its very possible that the crank sensor or camshaft sensor on the replacement engine is bad and giving you all the problems you have now.. are you using the original injectors? if you have injector pulses then check the coil for pulses the same way.. btw make sure you have 12v to them even before cranking engine could be a bad asd relay..wet plugs on one bank would also indicate a possible leaking injector and basicly draing the fuel starving the oposite bank for fuel.. to verify that the rail must be lifted by removing all 4 bolts make sure the clips hold the injectors firmly and turn the key to run but dont crank it then look for fuel leakin from bottom of injector(s) any drips is a bad injector..