Well they are pretty custom to start with, if it were me I'd go custom. Are you talking about the 4B or 4BT Cummins? I am sure some one has done it so there should be info out there,infact i think a guy on here posted one up cant remember exactly but it was a 4BT Toyota. I think you would be dollars ahead with a well built 22r or 22RE you could get around 20mpg.
