Efficient, plug&play and 300 hp won't go together very well in a MK2 Orion.
Any MK4 Escort engine (1,6 MFI/EFI and RST) will drop in without any issues, MK3 Fiesta (Zetec 130 hp) and later Escort Engines (Zetec 130 HP and RS2k 16V) also won't cause much troubles.
Given you REALLY want to go for 300 hp and your pockets are deep enough... 2,0 Zetec. Both silver and black top can deal with the same power. Just the Focus RS unit is a bit different as it's already turbocharged, running 215 bhp and can deal with a lot more. But once again... a Zetec Turbo is everything but efficient.
Hi XR2, first of all thanks for the advice! When I mean efficient, it's compared to the CVH engine. About 300hp is not my biggest concern, the idea is to have an engine that is easy to adapt, more modern and efficient (than the CVH) and that it can become a good setup for up to 300hp.
Thanks!