Jason,
Are you trying to mount the H60 with the front engine-mounted tank? If so, (suspected) it is a no go UNLESS... you modify (cut down) the tank mounting bracket to lower the tank height so it does not hit on the frame. Some Sears Ropers (The top of the line models) actually came from the factory with a Tec H50 which is the same size block your H60 HOWEVER... they used a remote tank mounted on top of the frame in front of the seat. (The only difference between a H50 and a H60 is the rod and the crank) My son had a "souped up" 1970 Sears Roper with a H50 which we restroked to an H60 and had a performance cam and heavier valve springs. That bike was WAY to fast for a Sears Roper which are already kind of squirrely as far as handling goes. If that H60 you have is a nice engine you might want to think about just modifying the tank bracket.
Michael