got a 38 scarab with 502's that shifts very hard had new plat. merc cables installed but i still need king kong to shift from forward to rev. any help

Pull the rear cap on the drive and have a look at the shift detent, and the shift linkage in the drive. Often the lack of lube will cause wear and result in hard shifting. Would assume you checked the shifter and new cable operation before reconnecting to the drive to make sure all was ok there. Sounds like the detent to me, lack of lube and possibly worn.

When you say hard to shift from F to R, be more specific...is it difficult to pull out of gear or difficult into gear. This info helps to get closer to cause.

it is difficult to shift into forward and to shift into reverse !! also checked the zero effort shifters - not the problem ..

Like RaggedEdge said the rear detent ball can cause shift problems rust an lack of lube,or if some one put to much lube behind the ball will make it hard to shift.