318 bogging at high rpm, but only in first gear?

1) If the distributor is factory, it was likely curved for 5* initial, and 30 degrees in the flyweights. for a total of 35Degrees..
With 18* initial now, you are trying to run 53* of Power-Timing, and the engine is complaining by detonation, which kills power.

2) With hi-compression heads on a low-compression short, you get an intermediate compression engine, that may be detonation-prone. It depends on where the Quench lands.

3) With 3.23 gears, Second gear works out to possibly 4500= 68mph, and 318s with factory springs usually float the valves about there, so perhaps you have a third problem.

Numbers 1 and 3 you can fix fairly easily.
But number 2 may require better octane gas than you can get at the pump. A high stall convertor, and/or more rear gear, and/or delayed max-ignition timing, may help. But if your Quench is in the zone of 050 to 080, it may not be fixable.
Happy HotRodding

But honestly, you gotta get the Power-Timing under control before anything..