89 F-250 Engine Change

I have an 89 F-250 with a 300 straight 6 that needs a new engine. I want to use this truck mainly for towing now so I was thinking about putting in a bigger engine. What would be the best choice? A 351? Is there a big block or a diesel that will fit? I've installed a few engines before but I'm not an expert. Thanks in advance.

The cheapest and IMO best thing to do is to install a carbed 460.

I would stick with the 300 if you plan on doing towing. It's got the TQ you will need. Putting in a Diesel engine would be nice and dandy, but it's not that easy..

Hey I'll sell you my 300 out of my 87 it it a good running solid engine, I need a tranny and can't afford it though.