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Maybe you would like some of us to just come and do it for you.
Changing and 300 for a 300 is basically no different than any other motor change out. To put a 351w in place of a 300 is more complicated. You'll need to cut out the old 300 motor supports and weld in new 351 supports. Bell housing & trans should bolt-up OK. Some electrical wiring will need work & other miscellenous items.
Check the local papers and salvage yards for a 300 or 351w for your project.