Hello.Yes,it is possible and not that big of a deal.However,if you have just put that 351C in your car,there are a couple of things you might want to check.The first time you close the hood,make sure that the stud sticking out of the top of the carb for the wing nut isn't going to poke a hole in the hood.The carb on a 351C sits a little higher than a 289 or 302.You will also need to make sure that the steering gear box won't crack the D/S exhaust manifold when you're going down the road.It should clear when you're installing them,so it's easy to overlook the fact that stuff is kind of bouncing around in there when your going down the road.Good luck!
I'd put the manifolds in before droping the engine in. Also make sure that the driverside manifold is for a 1970. The 1970 manifold has the rear port indented in for the steering box and is needed. I had to drop the steering box to fit the manifold in my car, I betb unbolting and lifting the engine would work as well, and it's a 70. The sad part is that I installed and removed the 2" primary full length headers without a hitch with the engine in. My car is a 351C 4v if that makes a difference.