Battery not strong enough for new engine

[82 GT]

Tonight I atrtached the ground strap from the firewall to the engine and still nothing but slow cranking.
I called my buddy on the phone and explained how I had things grounded and he quickly told me the problem.
I have the negative battery cable going to the frame of the car and he said that's not a good enough ground because itmust be grounded to the engine block.
I was too late for me to go back out and try it but I'm going to do that first thing after work tomorrow.
He said I need that grounding strap from the firewall to the engine and also the negative terminal to the engine as well.
Do you think that's what my whole problem is?
I'm hoping it is.