If you REALLY suspect a pushrod, it won't take you that long to inspect them, although I wouldn't take the pushrod problem as gospel yet - First, remove all the plugs (so you are not working against compression) and rotate the engine by hand (if you've got good arms) or with a breaker bar on the harmonic balancer. does it turn freely? is there any noises, clunking, places that offer resistance to turning etc? The engine should turn pretty free. Go through lots of revolutions and listen, the only sound should be air escaping from the plug holes. If all is well, then crank it with the starter - Still with the plugs out but disconnect either the coil center lead, or red B+ lead to the distributor (depending on if it's HEI or not) This will be VERY noisy, and although you may not THINK you will be able to hear anything, you are only looking for loud knocks here - if there is one, you'll hear it. If all is well here, the engine will spin pretty fast -faster than you'd be used to on a normal start. Next: Put everything back. Check all your fluids, oil, coolant, and start the engine normally. really, you might as well. It will tell you lots without a tear down - if it does throw a rod against the skirt then it was already done before you got the truck anyway. So now it's running (I hope) Do you hear a click, a knock, anything at no load idle? If you rev the motor with no load does the sound change? If you rev WITH load (in drive/first against the brakes)does the sound change? Connect a timing light - does the sound happen at the same intervals as the strobe or half as fast? Same interval means valvetrain - cam/lifter/pushrod/rocker. half speed is bottom end - rod/bearing/wrist pin/piston/cyl bore wear allowing the skirt to hit the bore - these will usually be louder under load. good luck. I'm not sure about where you are, but a Chev 350 goes for about $200 - $300 bucks here, often still in a running rust bucket (in my opinion the ONLY way to buy a used motor that you want to run as opposed to a "rebuildable core") Will keep watching your post to see how you're doing.
