Well, this is slightly off-topic, but since we're "blue-skying"
possibilities here, I thought I'd offer up my two favorite diesel
options:

1.  Mercedes OM602 2.5L 5 cyl turbodiesel.  It puts out 121hp in stock
form and can be bumped up to 350+hp with proper persuasion, and still
return 32-40mpg in MB sedans.  Probably tricky to impossible to
shoehorn in there under the lid, but I can still dream.

2.  Audi 5 cyl turbodiesels found in the first generation 5000 sedans.
 A bit low on hp and torque, but a few tweeks could fix that, and it
would fit relatively easily with the SA installation hardware.

Casey
Olympia, WA
Biodiesel:
'87 300TD intercooler (209k)
'84 300D (204k)
Gashuffer:
'89 Vanagon Wolfsburg Edition (185K)