the reason the 64-66 LA cranks are listed separately is because they have small convertor registers/hubs and will not accept the later[68&up] trans /convertors, however I'm pretty sure the OD of the register is the same for all years 'LA' so that flywheels will interchange in that aspect in all LA years.
2 ways to overcome this is ...to open up the ID of the register to accept the later '68&up tranny/convertor snout, or use the early tranny/convertor. BUT you can NOT fit later convertor guts into a early convertor case.
The other way around [newer crank to older trans/convertor] you can have the early convertor guts installed in a later convertor shell 'so that the splines match' , I've done this and had it cut for a higher stall at the same time=$179 total, or you can make a spacer.
just a fyi