Unstyled WC with WD45 block in it

Later this fall I picked up a unstyled WC that has a WD45 engine block in it.   I brought it in yesterday and would like to try to get it running again as it shouldn't take much as the engine is loose and has spark.   Just need to put a carb on it and run a temporary gas tank for now.    Was wondering though, the block is definately a WD45 block, but it has a WD serial number on the block.   Anyone have any suggestions to determining what I got other then pulling the engine apart, to determine if I have WD45 internals in it, or WD internals.   I am thinking that at one time the old engine block went back and this was it's replacement and it was during the time that 45 blocks were being made.   If all goes well, I am optimistic to have it running by the Packer game today, but we'll see.   I had spark etc. on it this fall before it got cold so it shouldn't be too hard. 

does it have the 45 head and distibutor or does it have the magneto mount, if every thing looks 45 I would bet it was a complete 45 motor somebody installed

WD45 engine #'s start with 45 ######. WD45 #'s range from about 0- 101415 while WD #'s range from 200775-358500.

Could be it was so close to the change over that they hadn't yet decided on their serial # sequence. Kind of like my Model C with engine #CE35 stamped on the back but all CE motors were supposed to be stamped on the flange. Never know with the early ones.

From what I undertstand, replacement blocks from A-C for the  WD and WD-45 tractors were all the later WD-45 blocks when the stock of the earlier block was depleted. I have a WD-45 with a block with no numbers; I assume the dealer (or owner) did not

I'm thinkin' that the 'factory replacement engine' is probably the most likely scenario.  That being the case, I think I'd leave it as-is.

if you have a friend that is an aviation mechanic,get him to boroscope it you can see lots of stuff with one.

It has the newer style manifold on it with a hole through the hood.   I was thinking of putting the old style manifold back on it and fixing the hood, but I'm not sure if the old style manifold is more restrictive then the newer style and plus with the taller head if the angled exhaust will still clear the hood's edge without modifying.   I'm on the fence as to what I'm going to do with this tractor.   I am seriously thinking of making a puller out of it, but if I do, I'm probably going to do some "mods" to the engine to make it a little more competitive around here seeing that noone else runs a "stock" tractor.  

I bought a 1941 WC whicth had WD45 bock.  The intrnals, head, mag. etc. were all Wc.  The block was obviously replaced.