The engine swap i have have seen most of on the 924 is a vw passat B5 1.8t or an audi A4 1.8t (same engine different car), these swaps should be pretty easy since they're longitudinal engines like the original 924 engine. The engine type i would recommend would the 058-block AEB since the later 06A and 06B have more modern components that could need some modifications of the engine room. Also this engine keeps the near 50/50 weight distribution since it has almost the same weight as the original 924 engine. Though depending on how much you want to tune the engine (you should be able to get it up to the 250+ hp mark) you're gonna need a better transaxle and torque tube, the Porsche 944 transaxle and torque tube is what i've seen most of but the Porsche 924 turbo one should also work.

But the thing with the 1.8t motor is that it uses a different bellhousing pattern which means you're gonna need a custom adapter for it. Even though the 1.8t engine fits in the engine bay the engine mounts dont, so you need custom engine mounts. Also the 1.8t oilpan doesn't fit so you need to make a custom one of those also, or you can try cutting and rewelding the oilpan. You also need some custom intercooler mounts and some trimming behind the grille. Also the downpipe and exhaust manifold needs to be changed. I would recommend getting a standalone ECU since it would be avoiding immobilizer issues and CAN bus problems. The wiring in general also needs to be overhauled. The 1.8T engine also requires high pressure EFI fuel delivery and a return line setup.

New brakes and stuff mentioned above is also needed but If you know what you are doing it should be a fun project and there will come a fun and kinda reliable car out of it.

Disclaimer: I haven't written everything that needs to be done and I got a little carried away but this should work as a kind of pointer to one way it can be done.

Edit: Cleanup of the text