Has anyone swapped a slant 6 into a 1938'ish car or truck original frame? Will it fit and how did you fab the mounts. etc. Thanks

Not exactly the same thing but you may want to look at Procycles build in the Sixers Gallery. There is a photo showing motor mounts on page 13, and other photos throughout the post.
That may give you some ideas.

_________________
Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

I can't remember if he ever posted pictures of it, but member Mongrel147 has a Slant in a 38 Plymouth. IIRC, the mounts were fairly simple.

_________________
Official Cookie and Mater Tormentor.

There is a 34 Dodge/Plymouth coupe with a Slant 6 owned by a board member.

A buddy of mine put a Slant in someone’s 3X? Sedan. I can ask him for some pics.

_________________
Rob

I’m Mater
The Kentucky Poser

There are plenty of more difficult swaps than a slant six in these old trucks. I'd go for it if that is what you want.

Canadian pickup models used the 25-inch six that I think was first used in 1937, but similar U.S. built pickups use the 23-inch (head length) motor. Chrysler Canada only used the longer six because of local content government laws. The Canadian light trucks and passenger cars used de-stroked versions of the longer Chrysler/DeSoto. I have a '47 pickup and have been told that the 25-inch six is a drop in with no frame or crossmember mods. That's not the case on U.S. passenger cars which need some front crossmember mods. The flatheads are compact motors, the slant six is actually kind of long. The OEM motor mounts were "floating power" that mount on the front of the motor with the sides free.

A fun swap was to use a bored 265 flathead where the 201/218/230 might have originally been used. When bored a common displacement is 282 cubic inches. Its not quick by today's standard, but it is pretty high in torque and will easily cruise at 70 mph all day long and has a nice 0 to 30 for city traffic. Everybody who sees it will think its a 218. The Canadian 218 was a de-stroked 236/251/265 - all the same block.