does anyone have an idea on cost to bore a cleavland block out to 40thou?
Wouldn't be that much, but normally 30 thou is the recognised safe limit of these thin walled blocks. Plenty of people have gone 40-60 but depending on desired planned power levels you could be inviting issues later.
I picked up my second hand unbored block for $80 and bored it to 30 thou.
But rough prices in answer to your question.........