From high boss head to low boss head questions
 

On my 123 with a k301 I went to replace the head gasket and found it was warped, and cracked. This head has high bosses. The replacement head is the higher compression head with the heart shape valve area and the depressed area over the cylinder. This head has low bosses. What is the proper way to bolt this new head down and still be able to use my heat shield and gas tank mount? I found spacers to put in the lower bosses but not sure if that is the proper way, or do I need to change to studs? I want to get this right the first time.

As per the parts manual for the 123, you also need a new/different baffle PN# KH-237677. (It's the part that you referred to as the heat shield.)