Re: 1961 XK with retrofitted 4.0L
What mounts are in there at the moment?
The engine mounts for the 250's are the same as 4.0's except the bolt pattern on the block is a few mm out. If you are using standard mounts for an 250 (XF style), just use the 4.0 mounts.
C4 will require a custom bellhousing. I got quotes between $450 and $600. Your other option is an XF/EA 3 speed borgy with a EA 3 speed bellhousing.
Heritage Green EF GLi
5 Speed, Wade 1521a, Headwork, Superlows, MS2 running fuel and spark