Are you 100 % positive the engine is spinning in the reverse direction? Make certain the flywheel is spinning backwards. Lift the car up and see if the wheels rotate in the reverse direction.

In order for this to happen your engine can not be a pull-start or roto start. It must be started by a starter box or possibly drill started without the use of a one-way bearing on a starter shaft.

Possible causes are, starter box spinning in the wrong direction.
using extremely short bursts while cranking the engine over with a starter box.

Since I highly doubt your engine is running backwards(although I have started OB boat engine backwards) I would check the flywheel and ensure it is secure.

Most sleeves can only be fitted one way only, by a key. No matter which way the sleeve is in will not cause fuel to enter any earlier than it would normally enter, as the exhaust port is always higher than the boost and side ports. Also, ignition is controlled by compression with heat not when the fuel enters the cylinder.

Ryan