Here is an easy option if there are dealers near your area that can help you out.
Buy a 83-90 toyota truck with the 22R 4cyl gasser engine and buy one with high miles like ready to die high for dirt cheap. Look for a engine dealer that will import a Toyota 2LII-T diesel engine from japan or from central america and they are a easy drop in. The 2LII-T diesel engine has the same engine mount spots as the 22R gasser and are an easy swap.
Someone has done it already.
http://vpizza.org/~jmeehan/toyotadiesel/