Trunk Mount Batt. Opinions needed

I tested mine like this. Hooked a jumper cable from the engine to the K-frame and boom, turned over great. Added welding cable as a ground from the K frame to the engine block and it has been good ever since

you should not ground to the K frame. It is "rustily" bolted to the body with somewhat rusty bolts!!!. Ground the engine to the WELDED parts of the unibody