The GM TKO will fit into your tunnel, your bellhousing, clutch components (pilot bearing, throwout bearing, clutch, etc), and will use your existing speedometer cable.
You will need to open up your existing shifter opening a bit. See pics here (click this link).
You do not need to move your console.
The driveshaft will need shortened about 2”, and the C4 or C6 slip yoke installed onto it. Would you like a brand new low cost aluminum driveshaft! Read more here!
Your crossmember will need modified, and moved rearward about 2”. Move the crossmember rearward such that the front bolt holes line up with the last bolt holes in the frame. Drill 2 new holes
for the rear bolt holes in the crossmember. The modification is to move the mount tab to the rearward side of the crossmember, as shown in these pics.
! See this page for a great write up with pictures by Mark Kafka! Thanks to Mark for providing the info!
If you’re replacing a 4sp in the ‘79, the speedo cable will be about 6” too short. Here’s a solution: There is a 2’ extension available for the
‘74-era 4sp. Also get the HELP (brand name) Speedometer cable kit. You can use both of these together to custom make the exact length speedo cable for your car. All for around $15.00.