I run stock 235 (not the stronger 261) springs on my daily driver 261 with milled 848 head and .433 net valve lift symmetrical reground 261 cam.
Plenty of spring left at full compression....see picture in the link.
4 years and 12K miles without problems.
Valve lift on the later 235 and 261 stock cams is pretty good:
261 solid cam (also used in late 235) is .416
late 235 hydraulic cam is .407
