So you want to de-stroke a 308???
253 and 308 both had the same stroke from the factory (3.06") so a crank that increases the stroke in one would also increase stroke in the other.
253 crankshafts have lighter counterweights to adjust for the smaller pistons. I suppose that if you could lighten the 308 pistons enough (ie. make them the same weight as the 253 pistons) then it might work?
You may also be able to get 'heavy metal' put into the counterweights to compensate if you can't take enough meat out of the pistons without weakening them (remember that the piston deck height will usually need to be accounted for as well)?
The lower the reciprocating mass, the better the responsiveness of the engine too, but it definitely won't be as smooth at idle.
Interesting concept though...
Andrew
P.S. The "cubic capacity" of an engine is simply the total swept volume of all the pistons, so...
((Area = π r²) x stroke) x No. of cylinders
If we do this calculation for a standard 308 we get...
Area of each 4" diameter piston = 12.57 square inches
(12.57 x 3.06) x 8 = 307.7136 cubic inches
So if you know the bore size that the block will end up with, and you know the stroke of your crank, you can easily work out what size motor you will have when all is said 'n done.