Main cap question?

The 273 caps are approx. 1.996 tall and the 340 caps will be approx. 2.247 tall. Same bore, but they may not line up exactly so if the fit is close they will need a line bore. The 340 caps are usually a few thousandths wider on the outside. Bolts are different length and 340 had special bolts for windage trays. The rear cap is the one that usually has the largest alignment difference so any swap of main caps can be problematic.