The b16a3 is actually the second generation b16 engine. It was only offered in the 94-95 del Sol vtecs, only 10% of all del sols (about 70,000 total, 7000 were VTEC) were ever produced. In 96-97 they swiched to the b16a2. It actually only produces 160 hp. The JDM version of this engine was the b16sirII, which had a tad more compression, less emissions stuff and better air intakes which gave it 168-70 hp (depending on who you talk to) Because of it rareity (if there is suck a word?) the b16asirII is a riser choice for a 5th gen civic/ first gen del sol.
The b16a, b16a2, a3, sir and SiR II are are baslicly the same engines just with minor diffrances, mainly being wireing. Putting a b16a in a 5th or a 6th gen civic is as about as easy as stealing the presidents limo.
as for putting b16's in civics, here are the rules
for a 4th gen civic/2nd gen rex, go with a b16a or b16aSiR engine (basicly the same)
For a 5th gen civic, go with a b16aSiRII, a3 or an a2 converted to run OBD1
For a 6th gen, your only option b16a2