Tires: G78-15 -> 215/75R15, 1970 ford galaxie, light trucks

Question
I have a 1970 Ford Galaxie.  From the factory it had G78-15's.  I know the closest modern sized tire to this is the 215/75R15.  Empty my car weighs in around 4000lbs.  Due to the weight of the car and the stiffer sidewalls on the older style tires i was thinking about placing LT tires on this car when when the current tires need replaced.  I went to a couple of tire shops in the area, I was told that the LT215/75R15 are too different in size to be placed on my car.

Would this conversion be appropriate to "return" the suspension of my car to closer to factory?  (stiffer sidewalls)

Would you recommend staying with P-series or would the LT-series be fine on a classic full sized car?  That has close to the same GVWR as the Light trucks w/ these tires.

Answer
Daryl,

Are you aware that Coker tire sells G78-15's?  Would that be a better solution?

If not, don't try using LT metrics.  They are quite different than P metrics and not at all suitable for a car such as yours.

Besides, I don't really understand what the problem with the P metric radial is?  What problem is it that you think is caused by a "soft sidewall"?