They are physically the same as the LN3, being the last of the Series I engines, aside from the slight difference in the rocker arm mounting. They have an extra approx. 5/8" hole, on each head, in the rail into the valve cover for the built in PCV system which works with the TPI naturally aspirated manifolds too. The LN3 doesn't have the same pcv system so the hole would need to be plugged, easily done, and an external pcv system installed. Beyond the roller rocker pivot difference, there is likely no advantage to using them. I will do a cleanup and mild porting, check the chamber cc's and try a flow test, but I suspect little to no difference. What I find advantageous would be the more universal nature of them when used on a Series I engine rather than cleaning up and porting for each engine. They would not work on a Series II engine, nor the reverse.