question does any one know of any problems with swapping early 302 W crank into 94 efi 302 W(now carby )am having balance problems as trying to fit in my boat with dog clutch,there fore not having balancer instead have a counter balanced hub read 28 0z not 50 0z as on efi motor any ideas

Check rear main seal ..
Yes the crank will have have same ballance so same flex plate/ flywheel and harmonic ballancer counter weight..

As you said early cranks are 28oz so you must use the early balancer/flywheel.
You'll need to machine the crank for 1 piece rear main.