Best low profile 383 dual plane aluminum intake?

Does your 383 already have a factory four barrel intake?
I am not sure there would be a good return on investment switching 516 heads to 915 heads if both have the same small exhaust valves, and switching factory cast iron four barrel intake for an older design aluminum version, since you mention the tight budget.
Of course you already have the heads, so it won't be too expensive to try it.
For your compression question, just wait to buy gaskets until you get the old heads off so you can measure the volume above the piston and calculate the compression ratio accurately, then select the head gaskets you need.