[TR] TR4A overdrive question

[don]

Hello TR folks,

I have posted a few times now.  I am new to the classic TRs, have 
only had a couple of TR8s in the Triumph range.  And a lot of MGs and 
a few Sprites and Morris Minors.  So I am dumb on TR4As, but now own one.

I have a potential purchase of an overdrive gearbox for $1,200 that 
is supposed to be rebuilt.

Can anyone tell me if the price is fair, and what dangers lurk here?

Thanks for any help you can give me!

Don Scott
Calistoga CA