When you build a 289, you need to make sure you fit flat pistons, from new only A & K codes had flat tops to get max. compression, but you still may need to face the heads to get the comp you want. AFR use 2 different exhuast valves to alter the chamber size. The valve heads are thicker for the 58cc head, chamber is actually the same. The overal comp will depend on deck height of the block, type of piston and overbore size ect. In real terms a set of 165 AFRs on 289 that is 30 over had the deck hieght checked and faced will getting up toward hi 9's 10:1 without taken anything of the heads, but the face on AFRs is quite thick, no trouble to take a cut off them. If you went to a 347 later 165 heads are not optimum, but they are not that bad either, they out flow simlar Edlebrocks that get bolted on a 347s all the time, and consider that they are way better than what a factory 351 windsor had from new, so it's still going go alright, just not as good as a set of 185's up high, having said we would not talking mega HP differeance here, in a street format. Likly about 20-30 hp in a street packages at around 6000rpm, depend a lot on the cam and rev range
I guess it comes down to what you want out of it. As long as you get the comp around 10 it will be fine, and may not need 98 fuel, due the alloy heads chamber design and the ability to get the heat away from the chamber better than the iron heads. Dynamic compression will depend on the cam. If you put them on a 347 later and want to drop the compression a bit you just change the exhaust valves. The exhaust flow is pretty much the same on 165/185. As is the intake at low lift. The 165's run out of flow at,a bit over 500Thou lift while the 185s keep flowing up to 600 thou, so this is something you need to consider when choosing a cam. no point running a cam with more then 550 lift if the head flow ends around here, it's only the duration that's working then.
The 185 use 2.02" inlet valve and bigger port to get the extra flow, the inlets are 100thou bigger then the 165 heads