[cycleguy55]

Detroit Bill may be on to something with the ball joint issue - that would certainly be consistent with the stiff steering. Once you've ruled that out I'd take a look at the drive train.

I know you described it as a front end shake, but as these are simple, short wheelbase cars with no sub-frame isolation, even something in the drive train can feel like it's happening elsewhere. As it sounds like the intensity varies with power levels, I'd start with the slip yoke from the transmission, all the way back. It could be a problem with a yoke, u-joint, drive shaft or pinion angle (as noted by Dwight).