Re: How involved is changing the powerhead....
Why buy a rebuilt block when you can do it for less? Once you have removed the electrical and gotten it to a bare block to replace, you can easily disassemble the block, have it bored and install oversized pistons for about 1/2 the price.
But my question is: WHY REPLACE AT ALL. You sound like you want to replace it as insurance. Many more engine problems are related to electrical and ignition problems than mechanical. SO: if the engine is running and giving no problems, replacing or rebuilding the block won't necessarily really provide you with more reliability. With modest care and maintenance, some of these engines will run damn near forever with few problems and no major breakdowns. "If it ain't broke, don't fix it"
Example: My 1969 Chrysler 55 was run for 8 days up to Canada and back at 8-10 hours running a day. I ran it for 15 hours straight and circumnavigated Manhattan Island. Never had a concern about a breakdown. I still own it and it still runs, although just this year it spun a rod bearing and I rebuilt it--But that was after thousands of running hours.
