Engine swap
Decide what sort of horsepower you plan on having as you may want to upgrade a few other things too......such as a transmission rebuild, better brakes, and stronger rear axle assembly if those haven't already been done. You'll also need to figure out the best exhaust system for that setup too. The stock exhaust manifolds are a choke point and have mismatch ports with 340 heads. Chassis headers can get a bit pricey these days, but, cutting the inner fenders for headers have tire clearance problems and would make me cringe. :soapbox: