It doesn't want a 6 cyl

[ohio]

Hello I'm new here. I have a 72 c10 step side.
When I bought the truck it had the original 3 on the tree and a 350.
According to the vin it originally had a 250 engine.

The 350 was toast. And I started to rebuild it. 4 years later I never did finish it. I just wanted the truck running. So i found a 250 from a 67 c10.

New clutch and flywheel, and using my original 3 speed and bellhousing.
And started to put it all in the truck. I set it where it is supposed to go. The bellhousing bolted to the rear mounts.

But the side engine mounts almost work but the problem is the crank is hitting the front most cross member on the frame. I'm stumped, why wouldn't this fit? This is the set up that the truck was supposed to have.
If the cross member was not in the way the engine perches would mate perfectly with the rubber motor mounts. If anybody can help let me know Thanks.