New Guy with Frame Questions

[Bri]

Hello All! I am a newby. I recently purchased someone else's unfinished project and I am tearing it down and starting over. I was told it is a Shell Valley Cobra body and frame. I have a couple of questions on the frame. The custom motor mounts are not level with each other (left to right). I'm including pictures to show the difference. In the last pic, you can see that it takes 1/2 inch of shims to bring it back into level. Is this normal, or is it a problem? If it is a problem, could it, or should it be fixed with shims? The engine will be a 302. Also, I'm thinking of removing the welded-in cross-member for the tranny support and replacing it with a bolted-in one for easier tranny removal. I'm concerned that this would reduce the strength of the frame if I should get into a crash. Would it be advisable to add-in some other cross-members for strength, and if so where would a good place for them be?