In the 50`s 60`s and early 70`s, power was measured by "Gross" meaning on a dyno, with no accessories such as water pump, etc. It was set for it`s best timing curve for power, the carb was set rich and no exhaust.
In the early 70`s that was changed to "net" which was timing set "safe" which means low as you could go and it run, the carb was set lean, full choked exhaust system, full accessories. So when a engine was done on a "gross" figure and made 300 horses, you put it on the "net" and that figure dropped to about 210. I never seen a 300 horse 350 with 441 heads, all the 300 horse 350`s I ever seen had 041 casting heads and some had 492`s. The 441 casting smogger head had large 76cc chambers and these usually came on engines making around the 250 mark only in "gross" specs. However, no, a carb don`t make a 50 horse difference. Cams were also different. The Cam used in 300 horse 327`s used since the early 60`s was used well into the 70`s and came in almost all base engines and some medium performance engines. That cam was used in the 283, the 307, the 327 and the 350. Later on when emission standards got more strict this cam was dropped from production even so it just about had round lobes.