There is a through shaft for the brake arm welded through the frame and I put the roller just in front (towards engine) and up (towards seat) of that through shaft.
Here is how I did it:
Put chain on bike
Leave alt cover off
Adjust chain with slack
Use punch as “shaft” through bearings on the roller
Get it right and smack the punch with a hammer
Drill hole size of bolt on roller
Mount it up, use washers or tubing to space roller to hit a nice and good on the chain
Thank you to Davmo for the tips on transmission build and use of the advancer(more on this later). Very kind of him to let me pick his brain for 30 min via phone call! Knowledgeable guy and gracious with his time.