Michael, if you use standard guides you sure won't need any heat.

If you try and ream the head chances are your going to ruin it. The method I use as I expressed works and saves those heads. By using the extra interferance fit the guide will conform to the slight irregularity of the hole. This will cause the inside of the guide to be slightly disturbed also. That is the reason for the reaming after installation. You can heat it if you need but using the proper MB drivers there really is no need. At the proper interferance it will go in about two to three times harder than the slightly oversize standard guides do in a virgin hole (one that hasn't dropped a guide - any movement is dropping in my mind). after near 30 years of doing this and hundreds and hundreds of heads, I only offer advise. If you don't do something on those droppers, it will be one short valve job. They will be slightly out of round and I'd love to see you match the head hole to one of the oversize 14.2 or 15.2 guides. Remember that after screwing the 14.2 there is only 14.4 remaining and then its a new head or some real heroics.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician