Hi SixInaRow . . .
The block casting numbers started to get longer in '48. The number for 48-49 235 block is 3835309. That head casting number is unusual. My '49 Chevy Master Parts catalog doesn't list it. I read some where that 838355 casting was used for the earliest '37 216 engines (which was a brand new design) and then was replaced by casting 838773 which was used through '40.
The 37-40 engines used domed pistons into a domed combustion chamber. In California Bill's book he indicates that the '37 to '40 head is useful on later blocks (with flat top pistons) because it will take an extreme mill job .187". On a 235 he indicates 8.4:1 compression with such treatment. But with such a heavy mill one needs to extensively re-work the side cover to get things to fit back together.
Your crank should have a casting number on the center weight. My Master Catalog lists the numbers as:
1933-36 837631
1937-39 838281 or 838877
1940-41 w/216 839111
1941 Y w/235 3660435
1942-47 w/216 839775
1942-47 w/235 839750
1948-49 w/216 3835271
1948-49 w/235 3835311
And my '52 Hollander Interchange shows:
1948-51 w/235 3835501
1950-51 w/235 Power Glide 3835513
Like HiTork says, there should be an engine serial number on a pad behind the dizzy:
it may be obscured by grease.
Keep us posted as you tear down. Great find!
regards,
stock49