The D16A8 engine is the equivalent to the ZC DOHC engine (non-vtec). The VTEC head from the D16Y8 will not bolt on. Neither will the head from a B16A1.
The head on the D16A8 is superior to that of the D16Y8 even without the VTEC. It flows better and really likes to be turbocharged. I suggest you turbocharge the engine instead of an engine swap. Cheaper and more power.
The stock D16A8 engine is will stand up to 250whp on stock pistons and rods. You can achieve that with a small turbo at about one bar. Anything else will require changing the internals.
A low cost way of improving the internals is to use Suzuki Vitara 1.6 pistons with some aftermarket rods.