Here's a Red Top SR20DET looking for a new home. Vendor row at the drags is a great way to make that JDM connection. Does the engine include wiring harness and ECU?
Beyond the tranny, the proper ECU, wiring harness and injectors are all possible points of contention. The ECU needs the correct input from the sensors, which is made possible via the wiring harness, and the injectors and ECU must be electronically compatible.
The ECU is key for swaps that bring VTEC into the equation and as a rule it's all about OBD (On Board Diagnostics). You want to use an engine and ECU with a similar OBD status. As an example, let's look at the B16A. B16A engines from 1988 to '91 are non OBD; B16As from 1992 to '95 are OBDI and 1996 to 2001 B16As are OBD II. The ECU should be of the same years of production as the engine it's controlling. Most surplus engine depots include the ECU with the engine purchase; if not, it's wise to purchase the correct ECU outright..
As for harnesses, there are connectors for the VTEC solenoids, a pressure switch, activation switch and a four-wire oxygen sensor that must be present to get the job done. In 1988 to 1991 Si models, these connectors must be wired into the existing OE loom. DX models of this vintage are more involved as you're converting a harness for a two-injector, throttle body injection system into a direct-port EFI harness with four injectors.
Beyond accommodating the additional injectors, the harness will require an injector resistor, magnetic pickup and accommodations for a B16 distributor. In 1992 to 1995 cars, the DX model requires the same modification as previous Si harnesses. The EX harness only needs to accommodate a knock sensor. Confused? Place Racing has custom harnesses for most Honda swaps and, priced from $150 to $300, they are worth every penny.
On the injector side of the equation, stick with the units that came with the engine. If this isn't possible, here are some tidbits from Russ Collins of RC Engineering.
From 1988 to 1991, Honda injectors were low-impedance, peak-and-hold units. In 1992, Honda converted to high-impedance, saturated injectors in Civics and Integras. Preludes and Accords made the jump to saturated in 1996. This area is where novices can really find themselves in a world of hurt. The ramifications of choosing wrong are a burned-out injector driver, which means a new ECU will have to be acquired. In some cases, the injector(s) get fried and at the very least mismatched injectors will result in a check engine light and a poor-running engine. A more complete overview of stock injectors in a multitude of sport compact vehicles can be seen in the accompanying Stock Injector Spotters Guide chart.
As with any complex undertaking, planning is key. Know exactly what components you need for your swap, then shop around. At some engine depots it's meatball surgery; engines are cut out of the car so quickly, the engine harness can be sliced up, ditto the radiator hose (which you need in a B-series swap, as it's larger than traditional Civic hoses).
Other questions for the engine depot should include throttle cable (B-series is longer that a DX unit), A/C compressor (different bolt patterns), fuel lines, heater hoses, engine mounts, shift linkage and slave cylinders. The bottom line is, you need to understand all the components needed to pull off the swap. One way around this is to purchase the entire front clip. The motor is still "in" the car, so it should be truly complete and you should have access to all the tidbits needed to get you down the road.
A power swap can be an intricate and intimidating endeavor, but the payoff is tremendous. Know your options. Know when to go with OE parts; know when aftermarket shortcut kits will save you time and money. Having a grasp on what it takes in parts, time and money will make the transition to big-league horsepower a smooth trip, whether you are doing the swap yourself or if you're having a shop handle the job.