Help me choose the best oil for a 41 Ford Flathead

[fdcg27]

That is a lovely old truck and must have been the hillbilly Cadillac of its day with all of that chrome trim. Clearly not the tradesman version.
Since you have the 15W-40 on hand, use it. It'll work well.
The main reason that straight grades would have been recommended new was that no multi grades existed.
OTOH, for a good weather occasional driver, there'd be nothing wrong with using an SAE 30.
We have a couple of members here who've recently run this grade in modern daily drivers with good results.

 

[randytrish]

I'm gonig to use the Rotella 15w40 I have for now. I don't have any history on the condition of this engine. Just looking at the condition of the truck underneath it looks as though the front suspension, brakes and so look to be new, although stored for 25 years. The engine and tranny are exceptionally clean and have been out of the truck. I wouldn't be surprised if I had a fresh engine. I hope that the previous owner will find the records of what his father had done during the two year restoration. It does not have an oil filter. It looks like there are a couple of options for an oil filter As far as the oil pressure. It had around 40psi cold. Ive only driven it a few minutes at a time. Move it from here to there, loading and unloading on the trailer. The tires are rotten. I'm going to check the brakes and lines and try and get some tires this week and drive it a little.

 

[BrocLuno]

Have fun