Finding an internal vacuum leak

Just went thru the same thing- rebuilt stock 318. I could not control the idle. It was sucking oil thru the ports due to the 318 Felpro gasket set gave me 360 ports. Now I had my 318 heads shaved 0.040” but intake was aligned. (Ld340 with FI fuel injection)
I was sucking 2quarts per 100 miles. Run great and I had about 1000 miles on engine after proper break in. Compression was perfect and leak down was perfect. Called summit and ordered specific 273/318 port gaskets- fixed my issues. Hope yours is as easy.