im guessing that this is why you have had a lot od looks and no replies ..
most people on here aren't engine builders ...
neither am i .. but if your building a high power RB26 .. i would suggest getting the head dechek to make sure its straight .. esp with a metal head gasket. while its getting decked, have them clean/bath/dip the head to get the carbon off it.
you will still need to clean the block with a blade and metho/turpentine to help get it clean.
if anything fell into the bore... i doub't it would go far into the gap between the piston and bore.. but blowing it out would be fine in my opinion.
oil feeds .. pretty sure that the RB26 already has one blocked.. a better idea would be to get the return drill out bigger to allow the oil to flow down better -- this recommended if it will be revving hard all the time.
if you dont get the head cleaned .. try carbie or contact cleaner .. works well on this sort of deposite
hope this helps you a bit!
Craved