Your guru needs his status revoked. The 304/345/392 Internationals are strong, tremendously durable engines, though any 304 & a 345/auto are a bit thin on power.
If the 383 is a Dodge engine, it's fine (if not, I have no idea what he's talking about).
The Ford/New Holland 6.6 is a good engine. It's a bit underpowered with an automatic (especially an Allison 545), but very durable, & can easily be turned up for more power.
The 7.3 International (aka the 444 V8; also it's smaller brother, the 6.9/420 V
is another durable engine--as used in 82-94 Ford trucks. The only weak spot is coolant: not using the correct additive can result in cavitation eating through the cylinders. If kept up, they just keep running and running.
Also, I've heard nothing bad about the International DT408 (no DT406, AFAIK), except that it's a bit thin on power, especially with an automatic. IIRC, it's a smaller version of the legendary DT466.
The only "avoid" list I'd have would be:
8.2 litre Detroit diesel (GMC, the occasional Ford)
9.0 litre International (IH only)
AT545 automatic transmission (any make or model)
Lucas-Girling hydraulic brakes (late-80's to early-90's Fords)
That's about it.