Hi Patrick,
Most people don't use break-in springs, except for performance engines. But, reducing load on an older design flat tappet cam during break-in helps (especially with the quality of many parts today).
For example, I checked out 12 of the latest Healey lifters and their cam lobe surfaces are flat (slight taper with NO crowning) and their diameters were often over-sized by up to 0.0015-inches by my measurements; about half of them were tight in the bores. They will need to be sized properly and then matched to the cam lobe profile/taper. However, both their side and lobe contact surface hardness did test within factory specifications.
I broke-in the engine in Barbie's TD with 80 pound seat pressure springs and then replaced them with 130 pound seat pressure springs afterwards. We put a lot of effort into her engine (billet crankshaft and rods, JE forged pistons, porting and custom valves, performance cam, high chrome liners, etc). And, it is a very nice and smooth engine with great performance. The engine machining was done by a shop that builds engines for museum restorations.
Collecting parts for the BJ8 engine now.
Regards, Bill