Guys, I know this is off topic, but what are the differences in the core engine components (block/crank/rods, etc)? A buddy with the 7.4 says they are the same engine. I can see the need for commonality due to cost, but a diesel is a different animal and is usually not too common with a gasser cousin . . .

As far as I know nothing in common; 6.5 is a Diesel built/designed from ground up as a Diesel.

Parts interchangability would have cast the 6.5L in a different light. Check out how much more 6.5L engine components cost compared to 7.4L.

Yeapper Bout the only things interchangeable between those two might be the GM stickers on the valve covers and bolt ons like the A/C compressor, alternator, and P/S pump.

The 6.2 and the 6.5TD are very simular. In fact, you can bolt 6.5TD heads, onto a 6.2 block. The 7.4 and 6.5TP share nothing in common.