Longhorn @4lbs? I doubt it.
My Jerry Jones is either 6.4lbs, or 6lbs, 4oz (can't remember which), my 56 bass is about 7lbs, my Chinese longhorn is in between. My homebuilt Dano Pro is in that same range.
They're all WAAAAY lighter than my jazz bass, which has to be 10-12 lbs.
I'm not sure if some people here at saying that 6.5-7lbs is too heavy, or too light? Send about right to me, anyway.

Regarding weight? My new-ish MIK Longhorn weighs in at 5.13 lbs.; slightly lighter than either of the 2 violin basses in the background. Both my 1st gen. MIK DC59 Pros weigh 6.11 lbs. And, yeah, there's a little neck dive with them - if you want to call holding up something the weight of an Egg MacMuffin "neck dive". Which, personally, I don't...
As for hum? None of mine have any that I can hear. I think the p/u's are reverse-wired - like people do to Rick's to cancel the hum. In any case, none of mine hum...
The tuning machines? Rather than the traditional guitar-style tuners on my Longhorn, the DC59 Pro's have normal Gotoh-style bass tuners (those, and the all metal, intonatable bridge, are what make them "Pros"). I just now measured the two headstocks - and they are identical. So, a tuner swap would be easy-peasy...
Using short scale TI JFs on a Longhorn? Well, the TI's are really too long - they're made for short scale basses with a lot of distance back to the tailpiece - like my MIK Rogue VB-100 (which is wearing medium scale Roto 88 Tapes in the picture). They're what most string makers now would call "Medium" scale. People
have had good luck with them on normal short scale basses -
with normal bass tuners. Flexible as they are, TIs seem to tolerate the speaking part of the string being wound on a large diameter bass tuner post fairly well. With the guitar style/size tuner posts on a Longhorn? Well... I'm willing to give it a try - if
you pay for the strings...
