You won't have to drill, they are fragile and will break real easy.
The next thing I do is pry each valve open and prop it open with a 7/16 diameter wood dowel (or just a bolt if no one's watching). Then i turn the engine upside down and tap the lifters up away from the cam. When that's done now the cam will slide out. The lifters will slide out the bottom of the bores when the cam is out, giving you more room to work on the guides.
Then I knock each valve guide down .100 or so with a valve guide driver like this
That makes it possible to get the guide retaining clips out without a lot of drama. When you have the clips out you can either drive the valve assembly up out of the block from the bottom or pry them out with a pickle fork.
Real stuck guides can be a headache. I've cut a few valve heads off with big bolt cutters so I can beat directly on the guide with a large drift. Some of the valve stems can be cut in the valley with bolt cutters, the end valves don't have enough access to reach the stem with the bolt cutters.
Edit - Looked at your photos again, you have the straight stem valves and one piece guides, that will allow you to pull the valves out of the guides and make all that much easier.
I don't know the 8BAs well enough to know all the differences, but I can offer the following -
'37 21 stud blocks look just like 59A blocks on the outside with a few exceptions. 37 and earlier blocks have 4 bulges in the pain rails where core plugs are installed, but that would only matter to a show car restorer.
32 to 36 blocks are very different on the front wall because of the lack of waterpumps in the block. There's just a lot less iron there, especially on the right bank. I can see that difference from 15 feet away when a car has the hood open. That doesn't make it unusable, just visually different and requires block off plates, how important that is is a personal matter to the owner.
8BAs have a different intake bolt pattern, with fewer bolts, but I think the same casting would work.
The bottom row of the 21 stud pattern limits the bore dia to about 3.188, maybe a little more. I understand the 24 stud change was made to allow the bores to be enlarged to accept sleeves in '38.
If I was to try to build a big bore 21 stud as a one off I'd ask you to move the bottom row of holes .125 or so then either try to get a set of Sharp heads made with the holes offset or plug and redrill a set of heads myself. But that would be a PITA for production parts, and require dealing with 2 suppliers. Maybe you're interested in making V8 heads too? A 24 stud waterpump head would make that all easier
Questions for the forum - 8BAs have different flywheels, they are much deeper than the pre 49 flywheels. Can you put a pre 49 flywheel on an 8BA crank and use a pre 49 starter?
What oil pan would you put on an 8BA block to put in a pre war car like my 36PU? What clearance problems would arise from that? What oil pump would you use?
What bellhousings are available to do this swap and make the engine and trans line up same as original, and will the front motor mounts work?
Will the 35-up breathers work on an 8BA, the scoop on the fuel pump stand and the breather in the front of the oil pan? I wouldn't want to put an 8BA draft tube in my intake manifold.