750 lbs? The only mopar engine that weighs anywhere near 750 lbs that's a possibility for these cars is a 426 street hemi. 273/318/340's are ~525 lbs, 360's are listed at 550 lbs, 361-400's are 620 lbs, 413-440's are 670lbs. And a 426 street hemi is ~765 lbs.
But all of those weights are factory stock, so if you're worried about your aluminum intake you're probably at least 20 lbs lighter than those numbers already.
The engine plate will be fine, even with an aluminum intake, as long as you don't shock load anything. Smooth and steady.