Either will work. The 270 heads are the larger Max Wedge port size so you'll most likely have to run an Indy 400-2 type intake since there aren't any other choices for low deck MW intakes. The 240 heads give you a lot more intake choices but you have to use the factory bathtub gasket which is a bit of a pain, or switch over to a semi-custom setup using a solid valley plate which is also a bit of a pain. The 270 heads are cleaner to install since you just bed them in a bead of RTV on top of the valley plate. Both heads use the same rocker arms and have the same exhaust ports. The 270 will make a little more power than the 240 heads but it probably isn't a huge difference. Maybe 30 to 50 hp more depending on the shortblock. Here is a set of 270 heads going on my 470 shortblock. We tested the 240 heads one day and then swapped over to the 270 heads the next day.
View attachment 1715038095