I've rebuilt quite a few engines over the last 50 years, both cast iron and aluminium, and not once have I ever retorqued the head bolts or nuts. And I've never had a problem. When you retorque, do you slacken off each nut in turn before reapplying the torque? If you don't you are unlikely to get a true reading. This Dolly 1850 is the first Triumph slant engine I have done. Why should I retorque the head? Explain it to me please.
I've also built more than a few engines in the last 47 years i've been in the trade, starting as a Triumph apprentice in 1970. Back then, retorquing the head was part of the first 1000 mile service on new cars, not just Triumphs, ALL new cars! And the practice continued until the late 80s introduction of laminar gaskets, stretch bolts and degree tightening. but whether a new factory engine, or a mere head gasket swap, older engines NEED a retorque. The slant Triumph motor is merely more sensitive to this than most! Long experience by many here has evolved the tecnique above, torque down head, run till at normal temp, cool overnight, retorque when cold, drive a good few miles (200-1000) then retorque again. You don't need to back the bolts and nuts off before retorquing, they will still tighten up a fair bit. Only a retorque after a long period of service need the nuts backing off first, to avoid the danger of "corrosion lock" Otherwise the head gasket you have sweated bullets to do may blow prematurely! I'm not sure WHY the slant is so finicky about this, but it certainly IS!
My running in procedure is very simple, drive to the nearest motorway and do 100 miles in your chosen direction at 50mph, then turn round and return at 60mph. Having completed this, change the oil and filter, retorque the head and go back to driving like you stole it! It's always worked for me!