I don't think you're "way off base" because you are trying to tie known guerrillas with Shanks' Regiment. I think there is a strong likelihood that Welch and his 30 comrades left Shanks' unit to ride to Jackson County in September or very early October. Since Shank's Regiment was part of Shelby's autumn 1863 raid, it appears Welch and company left that unit while the raid was ongoing. I still cannot rule out the possibility that these men were detailed back to their home area to recruit, as so many Missouri men were during the war.
Of the four men you mentioned the online military service records state:
--John T. Crump was from the Jackson County area;
--Gabriel C. Parr was from Blue Springs in Jackson County;
--Andrew Forgy Hays was from Blackburn on the Saline/Lafayette County area where Shelby recruited his 1000 men in August 1862;
--Maurice Jacobs was also from Lafayette County.
Add to these other guerrillas or relatives of guerrillas who also served in Shanks' Regiment that I found in MO State Archives:
--Frank Smith of Blue Springs served in Co. D, Shanks' Regt'
--David Hockensmith of Kansas City was in Co. C;
--Mart Rider of Jackson County was in Co. C;
--Joseph and William Helms of Jackson County were in Co. C;
--James Koger of Jackson County was in Co. C.
We may never know who most of the 30 were, but this is fun attempting it.