360 three speed manual?

im in the proccess of trying to fit a 360 out of a 79 3/4 ton truck that i rebuilt into my 73 swinger. the swinger is still a manual three speed on the floor and the truck was a granny four speed. the flywheel to the 360 is not fitting into the bell housing of the three speed, its actually about half and inch to wide. i am not sure whether there is another flywheel that fits into the three speed belhousing, or whether i need to buy a new belhousing alltogether. does anyone have any tips that could help me on this?