what is needed to put 4.5 inch bolt pattern on a 65 Barracuda

Assuming that it is a stock drivetrain/suspension, you have many options. Probably one of the cheapest upgrades would be to find an A-body 8 1/4 rear axle, which will require a slightly shorter driveshaft, and a '73 and later A-body single piston disk front brake system.

Or, I don't recommend, but you could purchase wheel adapters.