You may have the wrong starter OR the wrong bellhousing-clutch-flywheel setup. The bolt holes are supposed to be in line, not staggered. Aluminum nose is typical. The number stamped on the steel starter case does not need to match anything.
What starter did you pull out of there before? What are the last 3 digits cast into the bellhousing? "403"? or "621"? or something else?
-Mark.
