Most A15 engines can go easily to 78mm therefore using stock mazda B6 pistons is possible then you can have a non-interference type engine like factory mazda b6 was originally designed to be.
There is a bonus I found out recently on the miata forums that going Mazda B6 or Ford Laser B6, exhaust cam duration is 250 degrees and around 8.5mm lift, therefore miata peeps found a cheap way for performance cams. They use 2 exhausts cams ground to 270 degrees / 9.5mm lift, still using hydraulic lifters and springs and redline at 7800rpm. Cheap and great results.
Edit: Here is a link to a bp or 1.8L with stock non ported bp head and block
170+ hp at wheels from a 1.8L there is another build I can find atm
with 168hp atw in a 1.6L. Not bad considering 264/264 degrees & 10mm lift.
http://clubroadster.net/vb_forum/59-i ... ottom-end-no-porting.htmlvideo, sounds good
http://www.youtube.com/watch?v=t5qGAasccK8&feature=player_embeddedhttp://www.youtube.com/watch?v=9ye2Fn62xDc&feature=player_embedded