replacing rod bearings

Ok guys, motor ran fine before it sat for several years. Put back into my project vehicle and got it started after a few tries. Run and idles fine then all of a sudden i hear a knock when i first step on gas and/or when i rev it up to 2000 rpn. Goes away if i go higher. Pretty sure its the rod bearings but im going to pull the motor back out and take the oil pan off to make sure. I know i should do a full rebuild but then im short on cash (since i got to get tires for the truck in a few weeks) and was wandering if i can just replace the rod bearings while i have the oil pan off if it still looks good and has anyone done this