They are rated here at 210hp on Super fuel with the 327's dizzy, in the US at 200hp on regular fuel with a very slightly less "aggressive" advance curve.

The 307's heads are essentially the same head as the HK 327 and the cam and distributor and exhaust manifolds are identical.

The best way for me to explain it is by using the 1968 327 as an example. The bottom end on the 210hp, 250hp and 275hp 327's are the same. The 210hp and the 250hp use the same heads, but the 210hp has the 307's manifold and carby. The 250hp and 275hp share the same inlet and carby but the 275hp has Fuellie heads. The higher output 327's use bigger cams and lumpy top pistons.

So with a near standard cam and the stock 307 heads, with a 4BBL and Quadrajet you are going to be limited to around the 240/250hp mark (the 10ci difference won't make much difference). By using a pair of Fuellie heads (64cc 461, 462, 291 will look the part for the 1968 look but the 461 and 462 don't have the boss for the temperature sender) you'll get up near to 275hp. The 275hp 327 is rated at 10:1 but it is closer to 9.8, drop off about 0.1 for about 9.7:1 as a +60 307 rather than 4" bore. So the compression ratio will be close to a stock HJ 308. Going for a better cam and alloy manifold with a proper tune will probably see you closer to your 300hp goal. You could also use some aftermarket heads, or later 64cc style like 041, 186 or even the later slant plug style or Dart Iron heads if you aren't worried about it looking stock.

A HK dual exhaust will help heaps as well.

I just bought off Ebay (arrived yesterday) a pair of 1968 Quadrajets for 327/250, 327/275 and 350/295 - one is a Rochester Quadrajet 7028212 DH (auto) and the other is a Carter Quadrajet 7028213 DY (manual). These are the same carby as we got on the 1968 Pontiac/Impala and the HK GTS327 except ours were ordered pre 9/67 so we got 70272xx. They are also the same spec carbs as we got on HT-HG GTS350 except they came as 3 and 4 on the end rather than 2 and 3 as 1 and 2 were used for HT 308.

$200 is cheap for 461's. What they flow depends upon the 461 casting, there are a few types. Also if they have 2.02" inlet valves or 1.94". You don't want 2.02 on a 307 or even on a 327 really unless it is a race engine. The 461 casting is the one that comes in both 165cc and 172cc inlet runners, I think the bigger ones have 461X cast into them.

The normal 1.94 461's with a Edelbrock Performer, correctly setup ignition, a well tuned Quadrajet and a good exhaust will see you not far from 300hp (maybe 275-290?). You'll probably see about 170-200hp at the rear wheels but will depend upon the dyno. If you want more you are going to have to look at a better set of heads, more compression and cam which is what the 300hp - 375hp 327's had in the 60's but you will also have to think about the durability of the bottom end (rods, bolts etc). If you plan to go down that path i'd keep the 307 aside and go and find a 4 bolt 350 block (these can be had cheap on Ebay), a used 307/327 crank and build up a new motor using Vortec or aftermarket heads. I picked up a 4 bolt 1969 388 cast 4" short STD bore not long ago off Ebay for $250. Same block as a HT GTS350M but this one was out of a C10 truck.

Yes. 25hp. 032 heads are The McKinnon Industries version of the 290 head on the 250hp 327. The only difference between the 250hp and 275hp 327 is the heads, the 327/275 has 291 heads which are the same head as a 461/462 but with the sender hole.

Correct. And the 032 ports are 142cc and 59cc respectively vs the 165cc and 65cc for the standard 461, or 172cc and 65cc for the 461X.
The 461 also has 1.94" inlet valves vs the 1.72" on the 032. Some 461's have 2.02" and 1.6" valves.

Which would work better with the factory 2 barrel? Just for curiosity.

The problem with my build is i want to run the standard exhaust manifold with some light port work. If i can open them up to 2 and a quarter inch i maybe able to get the 300hp. Dont know which way to go. My 307 2 barrel engine is complete right down to factory air cleaner. Have to do some hard thinking. Only trying for 300hp but limiting myself to period items.

The higher power Corvette 327 manifolds were 2-1/2" I think. There are pretty good reproductions available from Dorman.
If they are much wider than the standard ones you may have an issue with clearance to the steering box on HK.
They also won't do the best they can unless you go to a 2-1/2" exhaust system all the way to the back.

Could maybe find a bit bigger 2 barrel carby that looks the same as your original and go 2 inch from manifolds and then connecting into a mandrel 2 1/4 with free flow muffler or go 2 1/2 from the connection.

I don't know about the 2 barrel Rochester carbys and all their sizes, but I know Ford have a hell of a lot of different size CFM 2 barrel options around, as I would think so do the Chevys.

If you find a bigger CFM one, you could open up the intake manifold body by grinding it bigger to suit the bigger CFM.

Just remember that 2 barrels CFM ratings are different to how the 4 barrels CFM rating are setup, a 500 CFM 2 barrel can make more power than a 500 CFM 4 barrel.

All this magic 300 HP figure is B/S it's all about performance how it performs, as two engines could make say 300 HP, but one performs much better than the other through the rev range.

Thanks guys