i dont know the dimensions of the newer stuff but the older ea series engines had a 92mm bore for 1.6 and 1.8 ea71, ea81 and ea82. basically the difference was in the stroke.
you could take the pistons from an spfi ea82 9.5:1 compression and put them in an ea71 block and yeaild a little better than 10:1 compression.
the 6 cyl er27 had the same bore and stroke as the ea82 but 2 more cylinders
the eg33 SVXmotor has a compression of 10:1 and i'm sure it would have the same bore as the modern ej engines, since subarus always remain consistent in design.
here's what the wikipedia says:
The EG engine was a direct replacement for the ER found in the Subaru XT sports car. Replacing it was the Subaru Alcyone SVX so Subaru needed a new engine. As with the ER27, Subaru took the EJ22 and stretched it two cylinders to make the new EG33. However, this four valve per cylinder engine was DOHC and used many valvetrain parts from the not yet released EJ25D.
* EG33: 3318cc DOHC, 230hp@5400 used in the 1992-1997 Subaru Alcyone SVX
Instead of stretching their current EJ20 as most might suspect, in 2000 Subaru did this family from the ground up. It is a totally new DOHC design using dual timing chains and coil-on-plug ignition. Nothing from these engines are interchangeable with any other Subaru engine as in the past. The EZ36 was introduced in 2008 to help the Tribeca's sluggish performance. It is a bored and stroked version of the EZ30.
* EZ30: 2999.6cc DOHC, 212-250hp found in 2000+ Subaru Outback H6, Legacy 3.0R, and Subaru Tribeca
* EZ36: 3564.3cc DOHC, 256@6000rpm 247lb-ft@4400rpm found in the 2008 Subaru Tribeca