Your 460 uses what's known as batch-fire injection, meaning it fires the fuel injectors 4 at a time and of those at least two cylinders don't need the fuel right away so it just kinda sits there until the intake valve opens and it gets sucked in the combustion chamber. 351 engines used the same setup as well. Always wondered why that was, considering the 302 had a true-SEFI (each injector fires separately from the others and only when needed) so technology was definitely there and already in use... Anyways supposedly the late 351s and 460s (IIRC '96-'97) got switched to SEFI setup like the 302s had, but I don't know that for a fact. If it is true, then you'll need a PCM from one of those vehicles, along w/ its engine wiring harness (or you can modify your factory one). Alternatively you can use a 302 PCM (already SEFI-enabled) and have it reflashed w/new air/fuel tables, heck if I know where or how you can get the data for those tho... Overall it's all definitely doable, tho not a simple plug-and play 5-minute job...
Actually that depends on the chip - the stuff that some 5.0 Mustang guys stick in their ECMs completely recalibrates them IIRC, w/ new load tables and such. And once you get into mass-air conversions you can really have some fun. Provided the ECM/PCM has the slot in it for the "chip", not all EEC-IV ones did. But I digress - on the '89 the OP is working w/ the best bet for cheap performance tuning is indeed base timing at the distributor. Not sure if he can pull whole 5 degrees over factory, generally on these older Fords anything over 12*BTDC is asking for trouble on 87 octane, his truck will have the knock sensor to limit the PCM-added advance so he has some safety nets there, but still I wouldn't go too crazy there. I'd say check where it is now, bump it up to 12, see how it works. Also put a gauge on the fuel rail, see what pressure looks like - no amount of fine tuning is gonna do any good if the basics ain't covered first.