Krusty - the torquing tip or rule of thumb that my Dad & Uncle taught me for tightening any of these things was: "opposite corners in thirds" - so you do a finger tight on everything, then step up in 1/3, 2/3, full or 3/3 of spec torque (some use 1/4's) going in turn to the bolts/nuts in the opposite corners - ro farthest opposite from each other, back & forth in an X pattern. Obviously with 3 or 5 etc. you need to improvise, but the patter is the same. Ergo, the factory manual instructions to which you refer, & never over-torque on a soft material such as aluminum or alloy parts (e.g.: heads).
IIRC - VW/Porsche changed the gasket material not eliminated them - although some "builders" apparently do what you mentioned Jake does or similar, but then I have half-zymers!
Lapped in or not, the purpose of a solid or applied gasket is to fill in the irregularities on the two surfaces & differential thermal cycling - which lapping doesn't address. While they may start out seating perfectly, over time the high heat at which these things run changes that, & the gasket material fill any voids as it heat cycles. The steel/iron cans & aluminum heads have different rates of temperature expansion/contraction, so that also varies as the engine temp cycles.
I can ask my long time mechanic Hans, who was factory trained on these before he came over here & opened his shop in HB. He knows a lot of the old history & what works & not with the stock set-ups.
However, it sounds like yours is the non-stock flavor.
One thing I do know to be careful about, is to use a gasket liquid/paste/spray which won't "eat" the aluminum in the heads, as some chemical formulations apparently wreak havoc due to electrolytic reactions - even if not acidic themselves.
You probably know that VW "discovered" that corrosion problem too late with their Vanagon waterboxers, where the combination of materials in their original coolant, case, cylinders/jackets, heads & gaskets caused the aluminum heads to eat away & lose coolant within about 40k miles (some as fast as 20k). They only partially rectified this problem with the 2.1 & the rebuild kits & coolant formulation in the mid-80's, as I know only too well, having now had 3 sets of heads on our 88 Westy over 200+ k miles (counting the factory originals)!