I painted my bus with cellulose but I didn't paint the engine bay.
2 pack is more resistant to petrol/thinners , fading etc.
2 pack however needs full body suit and proper ventilation to spray, most paint suppliers will not supply 2 pack if you don't have a spray booth (or can't prove you have access to one). 2 pack is a strong carcinogenic and is poisonous.
Celly is fine for most things, can get away with much less PPE with little to no adverse affects to health like 2 Pack has.
I presume the original was probably celly but I can't confirm this.
For what its worth I would lacquer the engine bay, lacquer is mainly for UV resistance and to reduce scratches to the paint coat. Engine bays can be high wear areas though if your taking carbs off etc every now and again, hence why I would lacquer it.