What do I do?

[Trunkster]

I guys, Just planning a winter project. I have a 2l air cooled. Very slow, under powered and lpg crap. It would be a shame to change the engine as I think keeping old air cooled on the road is the way to go. I was thinking of getting another van and converting it with a better engine but my machanical skills are limited. What should i do? Do I go for a watercooled and get a subaru engine or diesel van and put a caddy or golf engine in it? I dont want to break and land speed records I just want to sit on motorway at 65/70 mph with 30+ mpg. I have a machanic mate who can help me with all the tools. I thought about getting a donor subaru. Take the ecu and bits off it myself so I can see where all the bits go then help my mate swap the engine and gearbox. Is it as simple as that or am I on another planet? Any advice?
Thanx