Also, you mentioned going with a K20 because it is “newer”. Don’t think because B series are older that parts for them are hard to come by. There are so many parts for B series motors, but there are also a ton for K series as well.
Another thing to note about going K series is there will most likely be a lot more other work needed to be done to get it in the car. The mounts are different, shifter box/linkage is different, wiring is obviously different. I’m sure someone(or a few people) has/have done a K in one of these older civics, but mounts may be hard to come by unless they’re similar or can be used from another generation civic. Also, axles, they will be different and again I’m not sure about these older civics but you may need to get those made as well.
You’re right, there is a lot of fab needed to fit a k series. It’s not thy the engine is newer, it’s more of the appeal of a newer ecu, and parts associated with the k series. Keeping the b and making sure it’s well done may e the way to go…