Hard to say without more information, but in general the decreased compression from the larger chamber heads would probably drop it 10-20 hp from stock.
about 165 hp
About 280 horses.
Need to know the year.
305 horsepower
No. 305's have small valves due to the 305's small bore. Large valve heads can't be used on the 305 because the valves will hit the cylinder block. 350 heads breathe MUCH better than 305 heads. Stick with the 350 heads.
170hp at 4400rpm
305
The 1985 Buick Regal did not offer the 305 V8 as an option that year.
Either 145 with the base 305 4bbl or 165 with the 305 Crossfire injection option
Yes, they should bolt on just fine. Might get a little more low-speed torque with a decrease in top-end horsepower.
Yes they will, but 305 heads have a smaller combustion chamber so it may raise your compression ratio.
235 horse is stock on 98 305