[LOTF]

I had my Squier, which was originally a toploader, converted to through-the-body a couple of years back. My personal opinion is that both tone and sustain were noticeably improved but upgrading the pickups, which I'd previously done (thus ruling out that the improvement I perceived was due to the pickup upgrade) made much more of a difference. It didn't sound bad before but if I had it to do again, I would.

I probably wouldn't have done it on an '83 Fender, however, as it would have reduced its value. And I don't think being a toploader makes a Tele any less a Tele.