Both O-360-A and the IO-360-B series engines have parallel valves cylinders and are generally 180 hp. The IO-360-A series engines have heavier, more powerful Angle Valve cylinders (200hp.) Lycoming's TCDS lists the weights of the 0-360-A's around 258 pounds and the IO-360-B's around 268 pounds. IO-360-A with angle valve cylinders are around 296 pounds.
I have an experimental O-360-A engine that was build up with Bendix Mechanical Fuel Injection instead of a Carb. So its very similar to an IO-360-B series with a sump set up for a vertical mounted servo. I can't imagine 20 pounds extra for FI is right. I can see most of the extra weight coming from one engine driven fuel pump and one electric fuel pump. I can see the flow divider weighing about 2 pounds, and the I bet the servo is close to a MS carburetor. Ten pounds extra seems about right to me. But what do I know?
My engine with the Vetterman exhaust, two mufflers for heat, a BandC belt driven alternator and starter, one Bendix Magneto weighed 307 pounds, measured with a digital hanging scale.
An engine builder like Bob Barrows will build an experimental engine from Lycoming Parts to new engine tolerances for the experimental builder in accordance to what they desire, within reason. What kind of Cylinder? What kind of Fuel Delivery? What kind compression? Narrow or wide Deck case? Do you want a Prop Governor, Vacuum pad drive? You wont find a certificated low compression Angle Valve Carbureted engine, but Bob will build one to burn Auto Fuel.
Economics favor Fuel Injection significantly. Simplicity favors a Carb. Reliability - you tell me. I hear that EI eliminates the hot start issue. If I had a carb, it would eliminate the electric standby fuel pump. Then I could see leaving off the Alternator and have a battery operated electrical system for the starter, COMM radio, and maybe Lights for evening flight during civil twilight. But then I can't go as far, and it cost more fuel, and may loose some weight carrying capacity on long flights. Define your mission. I am an efficiency nut so I like FI with API balanced injectors to run lean of peak sparked with EI.