This is my first post here as a traveller seems to be on the cards for restoration

It belonged to a friend who had in on the road for some time and the main gripe of his was the lack of power. The 1275 conversion seems like a nice popular conversion and I am familiar with these engines. However, I notice that MG engines are generally favoured for ease of installation
How readily available are they and what is the ball park going rate on a ready engine?
There is never mention of mini donor engines. Obviously the gearbox dangling off the bottom of the engine won't help but are they too much effort to modify for a morris to bother with? i.e if one became available would it be worth going for it or holding out for the MG version?
Many thanks for help and wish me luck with the project!