Loud Knock under load

Hi all. I have a 99 Ranger 3.0/5spd that has a noticable knock at all speeds, but gets much worse under acceleration. Almost disappears when coasting. Only gets marginally quieter when warm vs. Cold. Here's some history: I recently bought this 80k mile truck from the original owner, a friend, with a seized motor (I got it very cheap). On teardown I found the oil pump drive gear at camshaft had worn thin and teeth broke, stopping the pump. The result was the front 2 mains had been lunched (but not spun thankfully), and the #1 rod bearing had stuck to crank and spun. The rest of engine appeared very good: no ridges at top of cylinders, rings looked good, a few piston skirts had some scoring below the rings, but cleaned up ok (and not a mark in the bores), cam was OK (its a roller) and rest of valveytrain looked pristeen. I am told the motor was run less than a minute after oil light came on. I replaced the crank with a good used one I had, had the rod resied and put a new set of bearings in. Carefully cleaned and reassembled (I'v done this many times in the past) - assembly went well, clearances were good, and assebled shortblock spun well by hand. This noise concerns me obviously.I am thinking it is a bad wrist pin (I would have maybe thought collapsed lifter, but I am guessing that would make the same noise under load or not) - any thoughts? I did try to check how fast the noise was. Using a timing light it appears to be timed with firing of the middle driver's side cylinder (ie: 1/4 engine speed).#5 I think. I have no budget to fix right now. Will drive it easy in the meantime. It runs smooth as glass, and performs well (if you turn the radio up. You'd never think there was a problem!) - Do get lost of looks though when accelerating from a light. I am going to start looking for a cheap relacement engine, or may pull and do a full rebuild on shortblock (bore out and put new pistons, etc). As soon as I can find the time and the cash (might be awhile). If it is a wrist pin as I think. How long can that last with easy driving? I have heard stories of them hammerring away for an awfully long time. Any comments will be appreciated THANKS