I just dropped the Advance Adapters NV3550 in my 68...very pleased with the fit and performance. Even drove from San Diego up to Paso Robles to pick it up and take a tour of the floor. But I digress. I took the Bronco to get it professionally tuned; the guys indicated that the ole 289 was pretty tired. I'm looking to replace the engine with something more fuel efficient since I put some miles on it when I head out to the desert. Thinking of a diesel but don't want to shove a 4BT. Anybody do any research on a Mercedes diesel? The cars are plentiful....and cheap...and I'm hoping a turbo charged 5 cylinder will fit under the hood.