Well let me try. I have personally swapped a number of these with no problems. All I did was the steam holes drilling on all but a couple. Those were to be used like a hot rod motor so I used heavier valve springs, not 261 factory but heavy duty from a cam grinder.
My take on this is that there is a theoretical need for heavier springs to follow the slightly steeper ramps on the cam. But, at the rpm we normally use a 50 year old motor, it is just not needed. Same for the guide specs, in heavy duty truck usage the added support is needed, but not for our use.
My dad and I used a 261 with an 848 head in a 51
Chev 1 ton for a wrecker daily for 5-6 years with no issues.
I think this was just a design for worst case use, trucks at fairly high rpm under heavy load for long periods. That is not the description of most Stovebolters usage.
