Just Some Dude in Jersey
A rebuilt to 2.0 with big valves is the most common and easiest route that most people have chosen. All your original stuff will fit it. I would have a nice new one right now, but I got talked into a rare 2.4 from Europe. PITA to get it all just right. Add to that the original, never available here, Opel Motronic FI system and you've got even more of a PITA. I'm just doing it for the challenge and to give me a nice long project to do.New Engine? Just curious, what does that cost?
Put a call out for someone to sell you a lightly used 2.0. You might be able to get one for less than a thousand. A big valve head and 2.0 block from Opel GT Source will cost you $2000 and you'll have to swap parts over from your old engine.
If you contact Goin Manta(Charles Goin), our current engine rebuilder, he might be able to give you a deal on a 2.0 or a rebuild to 2.0 of your present engine. Maybe $1500 or less. Or you can let him talk you into a 2.2/2.4 engine and then you can spend a bunch more money.