"how long is a piece of string??"

I agree with Dodgeman...you're wasting your time trying to stroke up an A15 in the <1600cc class. Besides, if you want a reliable A15 race motor on a budget then you can't afford to replace the crank with a custom steel unit, and you can't afford to reduce the bigend journal anymore than absolutely necessary. That is a weak point in the crank. I can show you photos of cracked journals if you need proof.

you can take the headwork "all the way" and end up with a slow engine if you don't match all your components together.

So what RPM is it?? 8000, 9000, 10000 ??? I would suggest you will struggle to keep an 8000 rpm engine reliable under race conditions unless you have a big budget and/or heaps of experience. The odd excersion to 7500/8000 rpm in a road car is different to holding it flat for minutes at a time. Chris Peto "the boss" has been racing his 1200 for..um...about 15 years or so??!? Dodgeman or Aiden might correct me here. he revs his to what sounds like 8000ish but also has created a lovely collection of boat anchors over the years - and that's when you know what you're doing. We limit ours to 7000rpm and have shelves of broken bits.

There's heaps of piston options. Thats why I asked you those questions before.

You asked for a guidline - as a starting point, why don't you consider the Wade 54/86 cam with twin 40's and a nice match-port manifold and extractors plus free flowing exhaust. The 1200GX head is a great performer especially if the ports are cleaned up (not increased). But you can port a standard oval port head to the same dimensions and use cut down L16 valves if you don't have a GX head. Double valve springs are a must to avoid piston to valve contact that will destroy your engine in a blink. Get a new set. I don't use roller rockers but Yella Terra sets are available from Repco. Others on this site have experience with them - try a search.