I put my engine together some years ago. I did what it says in the manual, tightened the rods so they fall slowly on their own weight when horizontal. Not very scientific, I know. I've taken up the first 3 rods since then. The 4th felt tight. Went driving yesterday and at higher speeds I could hear a knock. I suspect it's the 4th rod. I shorted the 4th cyl today at idle and you could hear it knocking. Isn't that the opposite of what is supposed to happen? I think I'll pull the inspection cover this weekend. I don't have the special wrench. Don't know if I can get to it or not. I'm a welder so I can make that wrench if I have to. But that would be indicative of the 4th rod being loose? I used plastigage on the 1st 3, but I'm not sure it'll be so easy on the 4th one. Here lately I've read a lot about taking out shims until it won't turn any more, then adding one shim (to both sides). The rods were new and have very few miles and the crank was reground. I think my fitting was poor.
Take out some shims and use timesaver on the bearing, it will give you the right clearance. Timesaver (yellow) makes fitting the babbit bearings a simple job. Lots of older threads about this.
over the years I have found often that if the rods need taking up often the centre main does as well. It will talk to you at full throttle and go away when more lightly loaded.
My approach has become to lift the engine out of the car , take the transmission cover and pan off, turn it upside down and do it once and do it right. If you half well equipped it is a one day job, and you can probably fix some oil leaks at the same time, maybe reline a brake band. I have reached a time where I just hate having oil drip in my face.
I know that I did nothing to the mains. I put them back exactly like they were. The babbitt looked good and I didn't know much about it then so I figure it was good. The mains probably are loose. I'm about to order some gaskets and check it out this weekend.