Not much difference. If you decide to revert back to a CA18DE. They still kick ass on an unworked A Series.

Engine Mounts are the same, between DE and DET. I had to make clearance for my turbo..But I had custom mounts, if you have the engine side brackets standard, then the DE engine will fit straight on the DET mounts.
The factory exhaust manifold should clear the steering, You may need to shim up a mount, or grind a flange to get clearance.

The Injectors are High impedance in the DE. The turbo ones are Low impedence and need the resistor pack (mounted on airbox) to suit the computer. If you've already wired up for DET, then you'll need to remove the resistor pack, and bridge some wires. You'll also need to remove the heated O2 sensor wires. Instead only the centre terminal is needed, the signal wire should be shielded all the way to the computer. Best suggestion, get a non-heated O2 senser wire from ANY CA20 wiring loom. Cut it at the computer and remove it completely from the loom. Even the 02 connector is the same as the CA18DE. Shouldn't cost more than $10 at Pick and Payless Blacktown. There's at least 20 cars with it, in the yard.

Everything else is the same.

Keeping the old engine and getting it rebuild is a good idea. I did the DE-> DET transplant in 4 days. And I had to remake one engine mount.

Chris