[sammyg2]

I put a V8 in a 914. Wil is correct on the weight.
A SBC with headers and an aluminum intake manifold and iron heads will be around 500 lbs.
With aluminium heads it will be closer to 450.
The flywheel I used was a modified 901 unit, no weight gain there.
The water pump weighed around 10 lbs if you include the pulley, belt, and hoses. not much of a big problem there.
The aluminium radiar and fans weighed not much, prolly less than 20 lbs or so.
Two gallons of water, 16 lbs.
it all ads up to more than a six, but not much more. Then you start subtracting the extra weight of the six besides the engine:
Oil tank, plus 12 quarts of oil vs. 5.
Front mounted oil cooler. Elaborate engine mounting bar in some cases,
etc.

I'd say the SBC with aluminium heads will weigh a little more than a 3.0 six installation after all is said and done but will run circles around the six.

The larger rear torsion bars were not to support the extra weight as the uniformed seller posted. They are used to handle the monstrous torque that is generated by even a mild chebby.

The SBC is so popular because they are cheap, reliable, and fit in small spaces better than almost all other V8s.
They are more popular than the V6's because high performance parts are easier to find and cheaper. They make much more power than a comparable V6. Installation of a V6 costs at least as much as a V8.
V6's are inherently flawed as far as balance goes. You can try to dampen the vibration or get creative, but all V6s vibrate more than a comperable V8. It's just the way it is. Some are btter than others.
A straight 6 is a much better design than a V6.

Having said all that and being someone who has BTDT, I would much prefer a Porsche six to a V8 in a Porsche.
A V8 car would be faster and stronger, but not as much fun in the long run.