W250 engine install woes

Did a clutch job on my brother's 91 W250. It's a 360 truck. Trying to put the engine back in and can't get it to seat. Get about a half inch between back of the motor and the bell housing and just can't make any progress. Rotating the engine internals doesn't make a difference, shaking it, pushing it, etc.
Are we missing something on the throw out bearing or something? We've confirmed that the new clutch splines line up and the pilot bushing fit over the input shaft prior to install on the engine (it should change slightly when installed so this isnt 100% perfect)