From what I've read an older engine that's already broken in should not have any issues with the new oils UNLESS it sees high rpm or heavy loads.
Adding a break in oil additive to your oil will help. Using oil that is rated for diesel will also hlep. They still have some of the additives that they removed from the oil rated only for gasoilne engines. Most all diesel rated oils are also safe for gas engines.
I use Shell Rotella 10-30W or 15W-40.

When installing and breaking in a new flat tappet cam you MUST use a break in oil or oil additive for the first couple of oil changes or the first 10K miles.

 

I use rotella 15 40 and lucas zink additive

 

Okay, I bought a 95 F350 motor F4TE motor out of Ft. Worth. So the motor comes in with the wrong emissions style. I need head style not manifold. One manifold was cracked. I' swapping in my good water pump never used, new oil pump, manifold due to plumbing differences, oil pan that's in much better shape, and my distributor. I can swap my dist without worrying about swapping the gears because low and behold my 91 has a F4TE block. This just gets weirder by the day. Now can anyone tell me who sells a lower radiator support other than LMC?

 

NO you need to swap the gear on the dizzy. a flat tappet cam used a different gear material then the roller cams. if you dont use the right dizzy gear it will shear and cause major damage.

 

To determine if a motor has a roller cam or not pull the drivers side valve cover off and shine a light down the front pushrod hole(may have to remove the rocker and pushrod.. which isn't a big deal), in any event if you see a dogbone around the lifter the motor has a roller cam and that means the distributor has a steel drive gear. Flat tappet cams use bronze or cast iron drive gears and obviously those wear out quickly if paired with a billet steel roller cam, so you don't want to do that. Here is what the dogbones look like...

 

The engine I just removed has F4TE cast in it. The new motor has F4TE cast in it. I cannot use the first motor's distributor? I know the truck is a 91, but someone had to have done a swap, right?

 

Yeah.. that means your truck has already had the motor replaced, and the distributor should already have a steel drive gear on it if the swap was done right the last time, but better safe than sorry.

 

You can also buy a reman'd distributor from you local parts store for a 96-97 F-250 5.8 and it will come with the steel gear pressed on it already.

As mentioned, removing the valve cover and taking a peak down any one of the pushrod holes will allow you to see if it has a retainer and dogbones for a roller cam.

 

Sorry for hacking this thread. I just pulled a 5.8 out a 93 e250 with f4te stamped on the block and it does not have the roller cam. I'm tearing it down now getting ready for the machine shop. Does the roller cam use different cam bearings?

 

No cam bearing are the same regardless.

 

Update:

Yesterday I had the truck towed to a different shop. In one day they diagnosed diesel fuel in the front tank, timing off, a few vacuum leaks, and a small egr issue. IT RUNS!! and runs very well. I was thinking that this truck was going to the salvage yard soon, but not now. I changed jobs and now have to get this thing ready to drive daily for a couple of months.

 

I recently purchased a salvage yard engine for my truck. Got one from a 95 E-350 van. It is indeed the f4te block. It's going to replace the worn out 351 in my 94 F-250. It came complete with intakes and distributor plus oil pan and all for $400 from a local U-pull it yard. Even better, they pulled it for me!!

The recommendation to go roller is simply why wouldn't you when you have the perfect opportunity to do an upgrade?

I've driven the older flat tappet vs the newer roller engines in pretty much identical trucks and I must agree. It's a much smoother easier revving engine. More desireable IMO.