The 300 is somewhat of a funny creature. I drove one for awhile and I enjoyed it. It continually stared in the face of impossible, rolled up its sleeves, and punched it in the face. We still have that truck in the family. But other motors do a good job as well. For your situation I think your choice of a 351 makes sense.

 

If your cam was going flat or is flat you would hear a rocker arm/lifter tick and it would misfire all the time not just under load.

Where are you seeing this pepper size metal particles at? Dip stick, oil out of the pan, cut open the oil filter?

Did you put a magnet to it and see if it’s magnetic? If it’s not magnetic then your looking at connecting rod bearings or main bearings.

Pepper size metal from a connecting rod, you will hear it. Pepper size metal from a main bearing and you will have low oil pressure.

 

We ran my pal's roller 351 on the stock truck 302 ECU, stock intake manifold. HO cam. Long tubes. Pretty basic setup, eventually found another used FMS MAF kit.

 

Long time ago I added some 1.6 ratio rockers to a 302HO and didn't follow procedures and cranked them down. When it wouldn't start from lack of compression I read instructions and re-did the torque procedures. 6 months later I lost cyl #4 and didn't know why till teardown after throwing a long block in it. Cam lobes were gon on #4. Had I known I could have changed cam, flushed engine and kept going. Most likely the cam metal will wash into pan and caught by screen and filter. Depends on how bad you need the truck as daily or intermittently.

 

Go for the 351, you won't regret it or look back. Since you already have a 302, it's a direct swap- even the 302 computer will run it. (You will eventually want the 351 computer though)

After owning many of these trucks, all with the six and a five speed, the 351 is where it's at. We've got a regular cab/Flareside truck with a 351 swap, also sports a 3.55 Trac-Loc with shorter than factory tires. It really scoots.