273 copper head gaskets SCE

Update ! after getting the 273 up and running again as I mentioned in a earlier post that I noticed the timing was at 13" initial . it has the fbo plate in a mopar electronic distributor ... so I set it according to what fbo says with the plate set at 14* and 20* initial for a total of 34* total timing . took it out for a spin and engine did not like that ... the hole car just shook violently . so I backed it down to 15* initial 29* total and it did not respond well and down on power. It seems that 13* is the happy spot but why is it so retarded at 27* total ? should be more like 32-34 total range . I even did it the old way by ear listening how the rpm rises when advancing dist and back off 2* and the result was 13 initial timing . . distributor has stock springs in it .