The TBI will not supply enough fuel for the magnum engine, it will run very lean as you push the accelerator. There is not enough flexibility in the programing to do that safely. If you insist on doing it wrong than at least get a 5.9 computer and throttle body from a full size truck, it will be closer to correct but still not right.

The knock off manifold is just as much a "hack job" as modifying and bolting on an LA intake, they are junk. The one I had would rock around in between the heads on a squaredecked block, it needed squared up it self, it was cheaper to buy the eddy and bolt it on than it was to buy and correct the knock off.

I have put LA performer intakes on magnum motors and the port was alighned decently as it was a smaller port dumping into a bigger port and with a thermoquad it ran awesome. It is also very easy to open up the ports a hair for even better alighnment.