After doing L18 research, parts availability and no history of the block, I ended up passing on the L18 and took a gamble on a L20B. It looks like everything is in decent shape for a 40 year old block, however I have not had chance to crack the head and timing chain cover. The previous owner purchased a package deal of engines and parts and the the only history he had on the L20B was the head was rebuilt. Can tell the a head rebuild by the cam shaft shims and the ports have been polished. Half of me is tempted to clean up the block, head replace the necessary parts from the L16 and get the 510 back on the road after 2 years in the garage. the other half -> the motor is out, a great time to deep dive into the motor, document what has been done and what needs to be done to get the motor in tip top shape.