> the flat 6 came in the mid to late '80's XT6 also.

The flat 6 in the XT6 was a 6 cyl version of the older 1.8 litre 4 and
was 2.7 litres (1.8 / 4 * 6).  The 6 in the SVX is based on the Legacy
2.2 litre and is 3.3 litres (2.2 / 4 * 6).  Maybe they'll make a
3.75 using the new 2.5 litre 4 (one can always hope)

There is a fair difference in HP between the 2.7 and 3.3 litre motors
The 3.3 is 230HP and if I remember right, the 2.7 in in the 140-150 range.
I'd think you would be better off using the 2.2 4 instead of the 2.7
as it is probably cheaper to maintain and is more common (and is a newer
design).  It is good for at least 135HP.

Dave