Let's see if you find this sort of thing useful. I'm no engineer - to be sure - just a guy who's been working on engines since he was a kid...
While the cylinders in the AMC242 are a bit larger than in the Ford302, they're not that much larger, as I recall, and that's really not the larger issue anyhow. As long as the rated delivery is comparable (there is a formula for correcting flow rate for different pressure - I just don't recall it offhand. I've got it, and I can look it up if you like...) you'll be fine. Recall that the fuel injector doesn't spray directly into the cylinder, so it's less of an issue than you think. Also, the AMC242 tends to run at lower crankshaft speeds than the Ford302, so that will also help keep things in line (most people cruise with their AMC242 down around 2000-3000rpm, while I've seen up around 4000rpm as typical for the 302. Hell, the AMC242 redlines right around 5500-6000rpm anyhow...)
Going with the later Ford or Chevvy injectors should help fuel mileage. As I recall, the Ford units have four spray holes (vice one for the AMC,) and the Chevvy units have either four or six. Since delivery is comparable, that means the spray holes are smaller - resulting in smaller fuel droplets and better atomisation. Since the fuel is more finely atomised, combustion may be more efficient (liquid gasoline is barely flammable, while vapourised gasoline borders on explosive. This is why fuel atomisation is so important, what makes FAE bombs work, and why - paradoxically - a full fuel can is somewhat safer than one that has just been emptied...)
Fuel injectors aren't specific to any particular "control system" - unless the electrical plus is different (in which case, you simply change the plug.) All a fuel injector is is a solenoid valve with a spray nozzle - not much to it. The only time you might run into trouble is if you have a "saturation" injector being replaced by a "peak and hold" injector - or the other way around - but that's an electrical difference. Production vehicles, as I recall, typically have "peak and hold" injectors, and should have resistance around 12-16 ohms when checked (I think. I'd have to look this up to be sure.) "Saturation" injectors are almost non-existant in production vehicles, so as long as your injectors are for production vehicles that are fairly common, you'll be fine (again, I may have the types reversed - but this can be verified fairly easily through the use of Google-Fu. The rest of the facts are good.) A lot of OBD-II SBFord injectors end up on RENIX rigs (which are "pre-OBD,") without incident.
Fuel metering is monitored by the oxygen sensor (HEGO) and is trimmed by the ECU altering the pulse width driving the injector - which changes the amount of time it's open, and the volume of fuel delivered. As long as you're not running past about 80% of the injector's total capacity (fuel injectors are typically rated for "delivery at 80% duty cycle anyhow," since you need to go larger if the thing is "locked open!") just don't need more fuel than the injector is rated to deliver. If you've got 19# units in, and you're consuming 20# per hour, get some 21# injectors and you'll be fine (you can also get 20# injectors, but there's no sense in not leaving yourself a little room.) I'd have to look up the equation for necessary fuel delivery - I've got that somewhere as well (it can be figured theoretically, using piston displacement; or it can be figured practically, using the airflow through the engine. The latter requires a dyno run or three.)
Short form? Go ahead and use the SBF/SBC injectors, you'll be fine. The XJ units are rated for 19-21#/hour, IIRC - while the SBC/SBF units are rated for 21-23#/hour. (I'd have to check. Both of these ratings are approximate, and would be for 39psig and 80% duty cycle. The SBC/SBF units would be a "corrected" flow rate, since I think they're actually rated up around 49psig.)
You're going to make me look up the maths, aren't you?:gee:
