[andyjboy]

James - the 2.5 litre short-stroke engine uses 90mm (2.7) barrels/pistons & a 66mm (2.0/2.2) stroke crankshaft to give a capacity of 2519cc.

Essentially there are 2 ways to achieve this:

1) start witha 2.7 engine (ideally with the 7R crankcases) & swap the crank for the 66mm version

2) start with an aluminium crankcase (from a 2.0 911 swb), get all the necessary machine work done (case squirters, bore spigots, etc) & add the 90mm barrels/pistons

This poses one of my original questions - which crankcase to use as the basis ?

The aluminium cases are heavier (but stronger) are now expensive (& becoming difficult to find) & will require quite a bit of machining whereas the 7R mag cases are lighter, cheaper/easier to find & have most of the required features already incorporated as std.