glsi 2.0 dohc is the i4 engine very different. 1800 sierra is a crapo cvh. Get a new transit 202 block or just a a good 205 block from alater sierra or tranny. You will need to change pistons and skim head to raise compression. Will need to open up the ports a lot. Will need new cams and manual followers. Then fueling to look at twin 45`s min.