1990 240SX KA24E idle problems after swap

[sil80drifter]

Here is the situation:
I have swapped an SOHC into my 90 240SX, as my other engine blew.
The only thing I've changed were the head and block (long block some would call it). The intake manifold remains the same. All of the sensors/equipment that were on the intake manifold remained there from the other engine, and before their setting allowed the car to run. I am running 460cc injectors with and SAFC, and the settings there also didn't change, as the car ran fine and idled before. The car is turboed, but the wastegate is left open, and this exact configuration ran fine before with the old engine.
I've done the timing chain on this swapped in engine, and as far as I know the engine is in decent condition, and has 70k miles on it.

So when everything was connected I've tried to start up the car. It has a hard time starting, and when it does, it idles at 2000 rpm, and bounces between 2000 and 2400 rpm and backfires crazily. The timing light shows timing around 15btdc (stock) then. It is not very responsive to throttle, and I cannot get it to revv higher than 4k. When I turn down the timing to around 0 BTDC, the engine idles more regularly, still around 2000rpm, and there is less backfire.
But, when the car is set at around 0 BTDC, it won't start at all, I guess the timing is too retarded.

I cannot figure it out. All the things are just the same. Could this be a timing chain issue (a tooth off)? I've done the chain quite a few times before, so it's not a likely thing to happen, but I guess not impossible.

The oddest thing about this idle is that my vacuum/boost gauge shows around 0 when this idle is going on. So this leads me to believe that something is really wrong. I just can't figure out what. I've pulled the water temp sensor plug and the idle got worse, as expected. All sparkplugs are firing and injectors are injecting, I've pulled them all in order and saw a definite difference. The only thing I didn't check was compression, but that doesn't seem to be a likely culprit.

Any help/advice is appreciated.
Thank you,

sil80