Q: can i istall a 1999 toyota pickup 2.7 engine into a 1996 toyota pickup and use the 1996 wiring and ignition?

According to the Toyota parts catalog, the short block used in the Tacoma from 1995 to 2004 is identical. That is, all those model years carry the same Toyota catalog part number, namely 1140075061. However, the cylinder head (the casting) in your present engine was only used from 1995 through 1997 (Toyota part number 1110179106). Note that 1997 is the last year a distributor was used in the Tacoma and that "may" account for a change in the casting, hence the 1997 cutoff for the head. I see though that the camshafts, valves and everything else installed on the cylinder head casting appears identical well beyond 1997-1999. Inasmuch as the short block IS identical for 1996 and 1999 what you could do, if there is no provision for a distributor in the 1999 engine, is simply unbolt the head from your 1996 engine (if still good of course) and attach it to the 1999 short block for a complete engine.

Inasmuch as you need an exact match (the engine is computer controlled; anything you use as an interchange for your 1996 MUST be exact in EVERY respect, otherwise you will have computer problems), another possibility is to simply conduct an interchange search at Car-Part.com. I looked up your 1996 application and I see quite a few exact engine interchanges for your 1996 engine listed at that website. If you are interested in an engine replacement, YourMechanic professionals in certain locales can assist with that. Please simply inquire based on your locale. If you have further questions or concerns, do not hesitate to re-contact YourMechanic.