If you're thinking about an engine swap, especially if the engine is an oddball (or if the car is an oddball) it would be nice to know how the weight of the prospective new engine compares to the old. And there are some newer engines starting to show up in the junkyards from the '80s and '90s when Detroit was getting concerned about weight, that might be lightweight gems, but there seems to be little published data.

For instance,

The LS1 should be lighter than an iron block SBC, but how much lighter than, say, an iron block 350 with aluminum heads?

The dirt cheap Cadillac 4.1/4.5/4.9L OHV V8 has an aluminum block (but iron heads). Is the 4.9 lighter than a 5.0 SBF with an iron block and iron heads? with aluminum heads?

And how much does a Northstar weigh? And is the 4.0L Aurora Northstar any lighter?

Just about any RWD car that came with a 4-cylinder will probably have enough room in the engine compartment for a V8, and certainly enough room for a V6. If I had a choice between an iron block V6 or an aluminum block V8, which would be lighter?

Is there a reliable source for this information or do I have to go to the U-pull with a hoist scale and pull engines just to weigh them?

Use the Shipping weight from Summit will get you within 5-10 pounds. don't use their phone to ask shipping weights though use their website so you dont tie an operator up and not buy anything though LOL.  

dunno about the rest but a ford 302 with iron heads weighs little more (a few kilos) than a ford 2.8 cologne v6 (these engines are known as 'boat anchors' this side of the pond), so v6's don't necesarily weigh less...

Hence why I'm ditching my cologne in favor of a 302.