Dumb question, but Will my 39 topload tranny bolt right up to a later flathead, like the one pictured?
Assuming that's an 8BA type flathead in the picture (it's pretty small), it will if you use an '49-early '51 Mercury or '48-52 Ford truck bellhousing. The Merc's are pressed steel while the truck bellhousings are cast iron. Make sure you get the starter plate that matches the bellhousing. The clutch will be a mixture of early and late parts.
As has been said the answer is yes IF you use the correct 49- early 1951 Merc stamped steel bellhousing with matching starter plate or the 1948-52 Ford truck cast iron bellhousing with matching starter plate. In my 40 Ford I used a 49-50 Merc stamped steel bellousing with matching Merc starter plate to bolt the stock 1940 Ford transmission to the 8BA engine A 1939 Ford top loader transmsiion would also have bolted up with no problems. I also used the stock 1940 Ford throwout bearing and the 1950 Merc flywheel along with the Merc 10 inch pressure plate and clutch. I also used a 1950 Merc rear sump oil pan to clear the tie rods. Make sure your flywheel iis drilled to fit the clutch and pressure plate you will be using. No need to use an 11 inch clutch. Lots more weight and your left leg will hate you. Be sure to read the info about installing an 8BA listed here. https://www.google.com/search?q=ins...60l2j33i299.8193j1j4&sourceid=chrome&ie=UTF-8
Make sure of what diameter clutch you use. The stamped Merc will only take up to a 10", while the cast truck bellhousing will accept all up to 11" clutches.