I am also curious how you are going to register that bike...
As previously mentioned, all pre 1970 Harleys are titled to the MOTOR ONLY. In fact, a real pre-1970 Harley frame does not even have a serial number... just a date code.
In Maryland, if you put a post- 1970 motor in a pre- 1970 frame you are required to re-title the vehicle as special construction, and the vehicle year ends up being the year that you apply for a title... so your bike may end up as a 2012...
Like you said, maybe Maine is less strict with such things...
I have run into this problem several times before, and here are they ways that I solved it:
1) I bought a titled Harley frame (post-1970), cut off the frame neck (where the VIN plate and serial numbers are) and then cut the neck off of the pre-1970 frame I wanted to use and welded the newer titled neck to the pre-1970 frame. Just make sure you do this in a frame jig so it ends up straight.
2) I bought a set of pre-1970 Harley engine cases with a title and swapped over all my motor parts into the old titled engine case. In my opinion, this is the way to go... and pre-1970 engine cases with titles show up on Ebay and Craigs List pretty often.
3) Part the bike out...