273 with 340 exhaust manifolds
The only slight drawback is the fact that the early 273 and 318 heads have a smaller exhaust port. This smaller exhaust port might give you some sealing problems. Some FABO members have got the manifolds to seal and some have trouble. I (69 318 Barracuda) swapped over to 302 heads to get the larger exhaust port and to avoid any sealing problems. If you place a 273/318 exhaust gasket next to a 340/360 mag gasket you'll see the difference right away (318 is the blue one). Also don't forget, the 70's 340 driver won't fit nearly as easy as the 60s 340 driver:
Treblig
The only slight drawback is the fact that the early 273 and 318 heads have a smaller exhaust port. This smaller exhaust port might give you some sealing problems. Some FABO members have got the manifolds to seal and some have trouble. I (69 318 Barracuda) swapped over to 302 heads to get the larger exhaust port and to avoid any sealing problems. If you place a 273/318 exhaust gasket next to a 340/360 mag gasket you'll see the difference right away (318 is the blue one). Also don't forget, the 70's 340 driver won't fit nearly as easy as the 60s 340 driver:
Treblig