I have an old 1990 civic hatchback that unfortunately is on its last cylinder after almost 20 years of service and 270k miles. A while ago I needed a new transmission at one point and my mechanic gave it a 5 speed.. no clue where it came from.. but aside from that it's been pretty much the same car my parents bought me.. I use it as a commuter car.. work is only 10 miles of mostly by uninterrupted freeway.. I was thinking it'd be kinda cool to switch out its engine for an hf engine and try and get the legendary 50mpg .. what would that entail? is that an easy thing.. and as it wouldn't cost me more than a couple thousand to do?