Yes 228 & 248 GMC motors have pistons that 'popup'
and come closer to the valves than 270-302
If you broke the cam thrust washer and the gear walks it will eventually machine the teeth off itself and valves can hit pistons.
In the GMC army manual they give a procedure for checking the cam timming in place but if your valves have touched you will not have any compression in the clys affected.
