My son's truck
 

We did the spider and fuel lines kit in his '94 S 10 4.3. Had to pull lower intake to get heat on the bolt that holds the fuel lines to intake. Had to pull distributor to remove intake. got it all buttoned up and it fired right up., shut it down until the next day, it was late. Next day I drove it up road and back, 1/4 mile total. Check gauge light came on showing low oil pressure, I turned it around ASAP and it died just before the driveway, had to drift in. Engine locked, won't turn over with starter or my hand. Removed plugs to check for hydro lock, cylinders dry. I pulled dizzy again to see it it would turn over. The dizzy was loose and spun easily. I watched my son tighten it, but didn't check that he got the hold down clamp over the bottom of the shaft. Nothing was holding the dizzy down! Spinning it a little in either direction doesn't change timing on these, computer controls timing. Would not having the clamp on dizzy allow it to raise up under acceleration just enough to disengage from the oil pump shaft? That's the only thing I an figure locked up this once decent engine!

Kinda seems that way.

Seems unlikely (to me) that it would lock up that hard in such a short distance. The bearing clearances in that 4.3 must be a lot tighter than old school engines.
Slick 50 or Motor Kote might have saved it. Give it another try after it cools down overnight.

FWIW, about 20 years ago I changed a spider on a 4.3 Astro van. I bought the GM part instead of buying an aftermarket part, so I didn't have to do the job twice. Well so much for paying more for the GM part thinking it was better quality. The new one filled up the engine up again with fuel almost as soon as it started up. The local GM dealer warranteed the part with another one, but I still had to do the labor twice.

Any possibility that the new part leaked as mine did? Running the engine with oil diluted with fuel could have finished it off.

I never dreamed the new GM part would leak worse than the original one with cracked plastic lines. It's a stupid design using platic lines that are constantly exposed to hot oil, and expecting them to last, then when they do fail you can lose and engine pretty fast if you don't catch it right away.

The distributor can be off as much as 20 degrees, and the ECM will compensate for it. You should use a scanner to reset the timing if you didn't mark it before removing it initially. Usually lifting the distributor up 1/8 inch or so, it should stay engaged in the oil pump shaft. But if the nylon guide collar split between the shaft, and the oil pump, the shaft can sometimes become disengaged from the pump from pulling the didtributor out. If that happened you could have the shaft jumped out of the pump tang, again causing no oil pressure. Those nylon sleeves tend to become brittle, and split when disturbed sometimes.

Never seen it on a 4.3 but we had a small block do that. Hold down was loose and we heard a noise, it was distributor bouncing up out of oil pump shaft.
I guess there is enough cam gear pressure to push up on distributor to disengage from pump drive if not calmed down properly.

New "rebuilt" spider (can't get new ones anymore for that year) was working great ran good idled great and no gas in oil. The nylon sleeve I did not know about, I will have to look down in at pump shaft. So the dizzy won't engage with the pump shaft without the sleeve? she is locked up solid. I have another engine that has low mileage and runs. Just need to find time for remove it from a truck, then transfer the upper end onto this "new" short block. just no time, and the kid can't do it alone.

Maybe you can get by with a crank and bearings and the pistons didn`t lock up in the bores. Maybe.