New to sirius and have a specific question

[wwotr]

My Father-In-Law gave me his "used" Sirius Sportster SP R2R for my 72 GMC Shortbed Fleetside.
I listened to Sirius XM in my Wifes 2005 GMC Sierra on a recent trip to Elko, NV last week.
I fell in love and was hooked.
I know that Sirius makes newer models of the sportster, but I was wondering if anyone was running the SP R2R in their 67-72 Chevy/GMC and how they liked it?
Is it true that reception is picked up (by Default) on 88.1 on the FM Dial of ANY Head Unit?
How/Where is the Magnetic Antena installed on YOUR Vehicle?
I'm trying to find out if I need a "Sirius Ready" Head Unit or can use any Head Unit as long as it gets 88.1 on the FM Dial?
I'd like to have it "Hard Wired" in as opposed to a Cigarette Lighter Plug in and have the Cradle hardware mounted under the Dash and have it so you can only see the Sirius unit below the dash. Then I'd have the Head Unit in the OEM Location in the dash, and Sound going to a Headliner unit that has speakers above the passenger/Driver as in the "Highliner" unit with built in speakers.
Roger