You may have hit the jackpot and found a B20E. If the center head bolt sits on a circular raised area that does not extend forward to the next fuel injector mount, it is one these much sought-after, high compression engines. You can plug the injector holes and mount SU carbs on it. If it came with an exhaust manifold, use that and hang a two-into-one downpipe from a 140 or 1800 on it. If you use your old SUs, you'll probably want to upgrade the needles to KD or DX to get the full benefit from the larger engine. Search the archives. There should be lots of information on this topic.
Bob S.