Trans Off 4-71 Detroit D - Help

[melodyoferror]

Hi guys nothing is ever easy first i bought a boat from thatEpay place then find the 4-71 Detroit in the boat has a stuck cam shaft .
Now to get that stuck shaft out is a major job as the flywheel housing must be exposed to remove the engine management gearing. But i have to take the transmition off this may sound wierd but i am stumped as i dont know what the tranny is or how its fixed on to the flywheel .
can anyone fill me in ;;
l have all the bolts on the G/box undone
And she will rotate but it wont slide back away from the D/D 4/71
I have used jacks between the mounts to try and give a bit of room for a wedge no luck there even with a bit of sledge hammer.
And ref to the bolt heads i can feel on the face of the flywheel there is no accsses for a spanner i think it maybe stuck by corossion in the spiget
Has anyone got any expieriance seperating engine from gearbox .
The 4/71 has only 900hr on the meter and the bearings are like new .but the boat was swamped and needs a full rebuild if only i could get that dam transmition off needless to say both moter and gearbox are old but can be still good again with a little bit of your expieriance 17/10/15 cheers hope to hear from you soon