You ask some well thought out questions, but I've found that this forum gets more responses when the question is 67-72 Suburban-specific. You have asked drivetrain questions that apply to nearly all 67-72 2wd GM trucks, whether pickups or burbs. If you find you don't get adequate responses to you good questions, feel free to post the exact same post on the Engine & Drivetrain board or the pickups board. HTH.
As to your transmission choice, the Getrag trannys have notoriously oiling & longevity problems. IMO, not worth using unless free. For me, not even if free. Just my preference.
You have a well-optioned burb, BTW. Congrats.
