Very heavy, but great tone. I have a '79 that I baught a couple years ago in NOS condition (still had the pickguard film with the control instructions on it.)
In response to the issues raised here...
Most early peaveys, including the t-40 have very stable necks because they are bilaminate with opposing grain. Look on the back of your t-40 and you can see that it is two pice, and the grain goes in opposite directions. It's not as attractive looking as a nice birdseye one piece, but it makes for good solid necks. Mine is super stable and it keeps a very low action very well.
It might not be great for slap because of the position of the neck pickup, though the spacing is nice and wide.
The T-40 is not an ideal jazz/fusion bass, a long cover set would be difficult due to the wieght, and older folks may do themselves back damage. For a rock and roll bassist, however, it may well be one of the best deals out their for those in search of a quality, vintage, american made, good sounding instrument, with a wide tonal range.
I can't think of a higher quality made in america instrument that can be had consistently for under 300 dollars. (with the exception of some other early peavey's)
My t-40 was my main stage bass (over my mim pbass) but now it is my standard practice space bass, and even though I play my 55-01 most of the time, sometimes it gets out on a gig because it sounds so good. It also sounds so good recorded, that I had an offer to purchase it by the sound engineer. I have no plans to ever part with it.
Conclusion: t-40's are great instruments, but without fail, they are ALWAYS HEAVY, and since they haven't been made in over 20 years, there is always the chance that something else has gone wrong, or been damaged.
You can download the original manual at the Peavey website.