Use 350 6X-4 castings
The 6X-4 heads were used on the 350 engines and have smaller chambers than the 6X used on the 400 engines.
By milling the heads & using flat top pistons with single valve reliefs and getting the pistons reasonably close to "zero deck" can get the compression to a "safe" 9/ 9.5:1.Careful cam selection is required.
The cam will actually determine the running or dynamic compression ratio the engine actually sees at certain rpms. Spark adv. curve will have to be adjusted to suit gearing, weight and operating range.
Push much past that compression range on today's "pump grade" motorfuels.
10:1 , 10.25:1 & points higher using stock cast iron heads without using a computerized engine management system is a crapshoot at best.Mandatory
big radiator, & trans cooler to keep operating temps from spiking.
An aluminum aftermarket head would be safer to attempt upper 9.75 to 10.5 static compression ratios. The aluminum is more forgiving that way because it dissipates heat faster.
Catalina is a heavy car and will have more of a tendency to Ping under load than a lighter car with the same or larger numerical ratio would.
I had a '63 Bonneville that did not like anything less than 98/96 octane gasoline. It was at 10.25:1 static . Large valve 1963 389 closed chamber heads w/600 cfm carter & stock cam for the 325 hp engine for that year.
It was a detonator 8 on lower octane gasolines.
Item of note: the federally mandated gasohols (e-85/e-15) actually have a slightly higher octane rating because of the alcohol in them.
However that does not translate into more power.
Alcohol does not make as much btu heat per pound as gasoline does but will resist detonation slightly better at higher compression ratios.
That may save your bacon if the compression ratio is a few points too high.
The trade off is Gasohols make less power per pound of fuel burned when used directly in engines that were originally designed to run expressly on real gasoline.
Mileage and power will suffer.
This happens even to late model electronic fuel injected cars & trucks.
I have a neighbor that owns a new Chevy truck and he said when he runs a tank full of E-15 fuel the thing is down on power & mileage.
He tows his desert toys with it and notices the difference on the mountain grades under load.
My current car uses a 400 @.030 over w/6x-4 heads that were milled .060
It runs on California 91 octane gasoline and has plenty of power.No pinging, no detonation,no dieseling / run on at shutdown.
Currently using a 2.73 gear. Lower 1st & 2nd planetary ratios to compensate that and still have 1:1 3rd and cruise economy.
Use an RP Quadra Jet , Carter Thermoquad or new Street Demon carb .
They work well if using a stock cast iron spread bore manifold.
Q jet & TQ will handle 750 to 800 cfm ,Street demon is avail in 650 & (now) 750 cfm.
Step Away From The KOOL AID !