Thanks guys. Guess I just have to get it up in the air and pull the pan. Even then I'm not sure how to tell the heavy rods from standard rods. I have to check and see if it has a weighted torque convertor in it as well. It's installed in a 77 D-100 swb. I bought this thing a couple of months ago and I'm finding out that the seller wasn't upfront with me about everything. He told me that it had an aftermarket .496 lift cam, and from what I can see, it doesn't look like the timing cover has been off the engine in 40 years. I keep finding things that don't add up or have been Mickey Moused on this thing. It seems to run well, but I can feel a vibration at low speed upon accelerating and decelerating. Also, at an idle in gear, the truck kind of jerks and bounces when you take your foot off the brake and let it idle forward. It's frustrating to say the least.
I didn't seem to notice a lot of vibration at speeds above 30 mph.