The "I've heard rumors that the S-10 front end is a bolt on" means that you have been talking to the wrong people. Guys have welded the S-10 front frame section on AD frames a few times but there are better options for donor rig front clips. To me subframing an AD is obsolute 80's cobble it together tech no matter what clip you use.
Donor rig wise Jag XJ around 1980) could be done pretty much as a bolt on if one thought it out.
Bolt on crossmember= the Chassis Engineering Inc unit that Heidts still sells or the Speedway clone is pretty simple.
Another option if the crossmember is available is the Indistrial Chassis inc Dakota crossmember. just under 1K now but Steve is having a hard time getting them built.
https://www.industrialchassisinc.com...ota-based-ifs/
https://www.industrialchassisinc.com/ is the brake upgrade.
It looks like he is back in a shop of his own and not working at Phoenix hot rods so the crossmembers might be available now or soon
https://www.facebook.com/industrialchassis/ I already have all the Dakota parts that i salvaged off a truck i bought and then sold to Woffords. the crossmember is a tad spendy but the Dakota parts should be pretty reasonable.