Simply measure your shell and see if the rad will fit. Or like alot of early rodders, just mount that rad out there with no shell.
To start the ID...if the 4 hose connections are same size, pre '49, if uppers are small '49 up. Many will have their prefix stamped into upper tank near hoses in fairly large letters, like 21A, 11C, etc. These will ID the application.
I have one for 28/29 shell in the for sale section that possibly could work with just a couple of outlets added.. But maybe not... Search 1928-29 radiator.... ---Sorry, had wrong search---
Sounds like you don't want to drop the bucks for a new radiator? Flathead? I would run a new one. Unless you want it to overheat..
Fitting a 40 radiator in a 28/29 radiator shell is like trying to put a square peg in a round hole,,it ain't gonna fit. HRP