Arghhh! There's no substitute for capacity! Thats true - but they're some pretty wild mods you mentioned. I've been there myself plenty times!!

We've had great success with 78mm. I would feel confident with a 79mm block IF it was ultrasoniced by a good machine shop and bored accordingly, and it has minimal corrosion. It doesn't make that much of a difference anyway. Overall power is limited by how much the head ports and valves will allow.

Thats why an A15 bored to 1600cc will never be capable of producing the same power and torque curves as an L16 is capable of. Bigger bore of L16 means bigger valves.

Manufacturers tend to use the long-stroke, small bore arrangement because it provides a greater thermal efficiency due to less exposed surface area for a given capacity. This helps with emissions. This is particularly true for motors made to a budget...ie when the engineers don't want to refine the motor too much or use expensive sensors and computer technology etc.

If you want a spacer block, I can CAD one up for you and have it machined here at work. Yuo should then bolt it too the block and bore the pair of them together!