Keep it straight 6. The engine compartment is might narrow on that 114 chassis, even a 280c. If you're going to go to a heavier motor, you'll need to consider better brakes, springs, new exhaust, tranny and the engine. Watch also for fun things like steering linkages being in the way.

There's another thread about somebody that swapped out a desiel 5-cylinder for a chevy v6.

-CTH