This first:
I'd suggest oil pressure leakage at the pump before excess loss at the rods. Your pump may have ingested foreign material or had a relief valve failure. There can be missing plugs at the end of an oil passage, I've seen broken castings on a pump etc, You might see bearing wear but it's the result of low pressure, not the cause.
It is quite common (i.e., I have seen it at LEAST 6 times) for the casting on the oil pump to become distorted (to something less than round) where the pressure regulator piston resides. This results in the symptom of: about 10 PSI oil when cold, less when hot. So, that's the first place I'd look if it were here. New oil pump body will fix it, or a run thru the zone where the piston is, with a drill bit of the proper (large) size, followed by some polishing of the results so the piston moves easily. When the piston gets stuck partway open it diverts most of the oil flow back to the crankcase and to the transmission via the cross-passage that comes into the tranny on the left side of the engine.
All this said: I have (and I will say UNDER DURESS) replaced crank main bearings and rod bearings w/o top end disassembly: I just removed the cam chain tensioner to get a little slack on the main bearings, then made a 'bearing puller' for the main bearings out of a screw (IIRC it was a short 1/4-28 screw, with the head cut down to less-than-bearing thickness, with the head thin and very polished, and it had a flat made on one side for 'pushing' with). I inserted it into the oiling hole of each main journal in succession and rotated the crank (use the alternator bolt, not the spark advancer's side, and sparkplugs out) toward the bearing's locktab side to slide it out, then oiled up the new one and started it in by hand, turning the crank back the other way, using the screw's head to nudge the new bearing in. The crank MUST be pulled up a little for this to work, hence the cam chain tensioner's removal beforehand, for a little chain slack.
The rod bearings were much harder to do, but managed to get them done: all the new bearings were Black size, replacing Green and Yellow ones.
All of this was an effort to salvage a rebuild someone else did, and he had just stuck in the same colors of bearings as were original on a K1 engine with 60k+ miles. The result was 10-15 PSI oil pressure at 5k RPM after warmup, not nearly enough to go touring. When given the choice, I will NEVER remove the cylinders from a freshly-rebuilt engine, as it will disturb the ring seating, from which it will not ever fully recover. Yes, it will run, but it won't be optimum.
I learned this technique from an old farmer who used to rebuild his own Ford-tractored engines (170 CID and 200 CID inline Sixes). He replaced the bearings 3 times on each one before he finally had them bored for new pistons and rings, and he showed me how. And his homemade 'bearing pushers', as he called them, that he made with a file and sandpaper!
