Welcome to the forum. :-)
There are a whole load of things that possibly spring to mind - but it is do-able. I am sure I have done it before but the way I would go about it is to take both engines out - place them side by side and do a detailed comparison. They are at heart the same engine - except perhaps be very careful as a little bit of knowledge can go along way. Now, please take everything I am about to tell you with a pinch of salt - as I normally go for 1.7 16v engines, but here goes.
If I recall the 1.5i.e probably runs on a distributor and everything that goes with it. The 1.6 possibly runs on a coil pack and so on. Therefore the oil pump in the 1.6 does not have the top part to turn a dizzy. Also the 1.6 has another sensor on the N/S cam to pick up engine timing (or is that just on the 145 / 6 16v) Hmmm..... think I am starting to get my engines a bit mixed up. Certainly there will be things that are different, perhaps things like front engine mounts and induction system. Saying that the block and heads should all be the same - so in my mind, it really depends on where you want to split things. Much easier if both engines are out of the car and on the ground.
Is it possible you could post a photo of both engines from the front and above and it would then be easier to quickly get an idea of the 2 engines.
Things like exhaust manifolds should be the same (both 8v) and other connections, but it is the complete inlet manifold, engine sensors, belts arrangements, V belt v polyvee belt (as you said) and so on, but then recently I changed my 16v engine to the flat (polyvee) belt arrangement - so that bit is certainly do able.
If you are fairly ok with spanners I would say go for it, but have a good check first. Certainly check what it is that is providing a spark to both engines and do you have everything from the 146 engine to go with it - loom, coil pack etc. Remember if it is the coil pack ignition you may have to swap the oil pump from the 1.51.e. engine if you were going to keep the original induction system.
Have a really good poke around first, check fuel lines, injector rails, TPS connections, loom connections - everything, then decide at what point you are going to separate one engine and all its controls and join them to the other engine.
Perhaps others who know these 2 engines better can comment....