273 Stroker, 4.00" Crank
Not any more clearance issues than a 340/360 except for the fact that the 273 bores are smaller and may require more clearance at the bottom of the bores. The biggest problem is the pistons. No one makes stroker pistons for 273's. There are companies that make stroker pistons for the 318, 340, and 360. I don't know the ins and outs of bore vs. stroke when it comes to horsepower and torque but there is a benefit to stroking small cube engines. Hopefully someone will chime in with more information.
tmm