Yep - there were some 406 engines built that had cross bolted mains - I had a late '63 XL 2 dr hardtop. The whole engine was a mish mash of strange parts, that included the mains plus 427 long style headers. These were not someone elses add-ons because I bought the car new. Unfortunately, in my infinite wisdom I traded the car for a new '65XL w/390/330 solid lifter interceptor engine - what a big disappointment after the 406 - that entire car was a Monday built piece of junk.