Help[ !! What happened here?

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I just experienced an unusual event with the engine of one of my old Chev trucks (‘71 C20/SB350) and am thinking that some of you may have had, or heard about, the same kind of thing. Before I start in to diagnose and fix the problem, I would like to benefit from your knowledge/experience.

As background and with the thought that many of you have experienced the bad outcomes of ethanol sitting in our gas tanks and fuel lines, due to a prolonged recovery from a health matter I was not able to run most of my trucks for quite a while. So, then spent a lot of time and effort – and some $ - dealing with the corrosion/particles formed due to ethanol absorbed moisture in the OE fuel tanks and collected in fuel filters and carbs, not to mention damage to fuel lines, fuel pumps, etc..

I have been moving my trucks to a new home and this was the final one – 250 mile drive from rather high elevation to desert - and all went just fine for the initial 150 miles from cool morning to mid-day 95+ degree temps. Engine running easy/quiet with excellent output (pulling a 1500 lb. trailer) – and normal amps/temp/oil pressure. Periodic stops to check the loads, hitches, tires, etc. showed zero leaks or problems. But, the fuel gauge seemed to be dropping more than expected.

After a short stop at a rest area and then running about 10 minutes at 60 mph on an interstate, the trailing partner on radio saw a sizable puff of blue smoke from under my truck which then tapered away, and also smelled something like petro burning – and I smelled the same thing. Oil pressure dropped slightly. Stopped at the first good opportunity and found plenty of oil on the pass side of engine and dripping from the frame – level on dipstick slightly below “add” and dipstick holder out of its hole in the block. Oil leak seems to be coming from the joint between oil pan and block in middle of pass side of engine. I am figuring a blown gasket there. After adding oil and trying to drive it a bit further (good oil pressure), a stop to check showed continued leaking. Hauled the whole rig home on a 40 ft. trailer.

Now – please evaluate my guesswork and/or tell me your diagnosis before I tackle the job. I think that ethanol damage had caused an opening in the diaphragm of the fuel pump and that it was pumping fuel into the crankcase and, after accumulation of fuel and heat in there, a sudden flaming or explosion caused the blowout of the dipstick holder and pan gasket – and the escaping blue smoke. Or???

Thanks in advance for any replies/advice.