I have a 1990 T25 Caravelle with a piddly little 1.6 Seat Diesel engine in the back, and to be honest, it's not great

I'm in the process of fitting the van out at the moment with the usual stuff - rock n roll bed, water tank, cooker etc etc, and naturally, the overall weight will be increasing quite a bit, so i need an engine that will provide more power/torque than I have right now, particularly as I'm planning lots of trips to the coast inclusive of some pretty steep inclines.
I'd really like a Subaru 2.2 Legacy engine, but dont feel it will be cost effective on the fuel side of things, so keeping things sensible, I'm thinking of a VW engine.
I suppose the simple question is, which is best? And if somebody could suggest somewhere failry close to Birmingham that could supply/fit, that would be really helpful

Mark