Trick flow 240 or 270 for 421 big block
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.
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.