With Christmas preparations, I seem to be getting nothing done airgun-wise lately, so if you are able to make some progress, please share. Learning is always easier with a collaborator.
I think getting the new scope rail parallel is tricky but nothing that careful measurements and execution can't overcome, since the scope itself has some adjustability to compensate for slight variations. There are also adjustable scope mounts, although they are quite pricy for this gun.
I worry most about getting it parallel in the horizontal plane (i.e. getting the wood cut and leveled correctly). Maybe you have some ideas about how you are going to do that. I was thinking with a table saw and a lot of fixturing, so I could do it in one pass, once set up for the cut.
Once you have that problem knocked out, others have shown that mounting the rail on the now-parallel surface is something you can do with just a little care. Blogger Derrick38 shows how he added a scope rail to a AK B-3 here: http://anotherairgunblog.blogspot.com/2009/09/bam-b3-1-tune-up-part-3.html.
Also, just the other day, Scot Laughlin briefly described how he mounted a weaver rail to a TS-45 in this thread: http://www.network54.com/Forum/113813/thread/1323542773/TS45%2C+first+tear-down
Good Luck! I'll post my solution when I get it finished or at least started!
PS - I was also thinking about a M4 type "quad rail" mounted on the gun. You can pick nice aluminum ones up off ebay for less than $30 shipped....