There's always the Cadillac 4.1/4.5/4.9 engines, aluminum block, almost 300 ft lbs without even doing anything to it, and they're pretty easy to find in a junkyard. Downside is they have iron heads. Yeah that's right, aluminum block with iron heads, beats me, why have an alloy block and iron heads they say it's for durability but it's not as if aluminum heads are anything new and this isn't a very old design anyway. Might be a candidate if aluminum heads are available though, that should put it in the 450 lb range I'd guess. Bolts up to the GM 60 degree tranny pattern too (pretty popular with the v6 fiero guys as far as conversions go). Downsides, it weighs about 500 lbs for the long block, the 60 degree v6 is about 350 lbs. Stock G16 8v is what maybe 250-300 tops? (I can lift a long block myself so I'd lean toward it being closer to 250 if even that much though) The Caddy v8 has wet cylinder liners that aren't cast into the block. Sounds like a complete nightmare to rebuild. It costs more than the dime a dozen 60 degree v6's do both up front and for parts. With all the Cavaliers, Camaros, Firebirds, Isuzus, Luminas, Berettas, Corsicas, Malibus(I think anway) etc using the 60 degree v6, it's just flat out easier to find and parts are much cheaper and easy to find. The 60 degree v6 also will happily rev to 7000 RPM without any real modifications which matches the 1.6 8v's 6500 RPM redline pretty nicely. It's also much easier to get performance parts for than the caddy v8.
Why not a 4.3? 60 degree v6's are inherently balanced just like a straight or flat 6 is. (Bunch of trigonometry and the degrees between cylinders at TDC in the 720 degree engine cycle), 90 degree v6's like the 4.3 aren't inherently balanced although a 90 degree v8 is. All things considered a 60 degree v6 will be less inclined to eat itself as time goes by compared to a 90 degree v6. The 4.3 weighs a little bit more at about 450. A small block is about 550. Might save a little with aluminum heads or if you can afford it a bowtie block.
A mildly built 60 degree engine is more than enough power for a kick/track/sammy anyway really, not trying to build a drag racer, just a reliable 150-200 HP engine that still nets OK mileage with an overdrive transmission and big tires but still is able to pass on the freeway. It's also more compact to fit where an I-4 engine was. The 4.3 can fit too but it's quite a bit wider. Also, since the 60 degree was used in the firebird/camaro, it's easily found attached to a 4L60 tranny. (granted the 4.3 is too). Slap some aluminum heads off a newer front drive car with the 60 degree and you can shave off a few lbs as well as run higher compression.
If the caddy V8 (non northstar) weighed less by way of aluminum heads I'd maybe consider it. Also there's the Olds Aurora 4.0 V8 that's the baby brother of the Northstar, might weigh a little bit less.
500 HP in a tracker/kick/sammy would seriously make me crap my pants. Way too much power for that small of a vehicle considering it's relatively high center of gravity. (although 500 HP in my 2400 lb Datsun 240Z is quite fine, but it's also much less prone to rollovers)
I just think for the relative ease of the swap the 60 degree v6 probably can't be beat except by the 4.3 or a smallblock in terms of bang for the buck and they're probably too heavy.
That's why I like the 60 degree V6 anyway.
