L31 swap for my 72 K20

[The Blue Pig]

Hello! I finally made up my mind. I was at a local impound auction yesterday and purchased a 99 Suburban (was involved in an armed standoff with local law enforcement a little over a year ago). After I paid my $450, I changed one flat tire, hooked up my jump pack and it fired right up after sitting for 15 months. Anyways, I have an engine in my K20 that runs just fine, quadrajet, 350 trans, NP205. I have no real interest in performance, tire roasting, hill climbing or anything like that. Just one turn of the key, no choke, no 5 MPG, not BS. Just go, and once to speed, go in OD!

I know that this swap is becoming less and less popular, being as it's somewhat old tech and the LS swaps are the big thing now but I bought what was cheap, somewhat straight forward and available. In fact, after searching and searching for weeks, I have found that information on this project is sparse. I know that the 4L60E will necessitate the moving of the T-case back, driveshaft modification, possibly shifter/floor modifications, etc.

What I am not super clear on is:
1) I need to get the ECM flashed? And if so, what items are the items that need to be deleted for this project?
2) How does one get around the loss of a mechanical speedometer input, or can I just expect to have to buy new digital gauges? I'm not really interested in some flashy, ridiculous gauge set. Just as close to factory as possible would be my preference.
3) Everyone "claims" that this project will bolt right in, however, in my current configuration, the manifolds are like, 1/4 inch away from the engine mount bracketry. Will the engine truly fit directly in, or should I plan on putting other manifolds on before I drop it in the cradle?

Anyone who has done this, please, let me know what you experienced! This will all be a learning process but I sure don't want it to take 5 years to get done! Haha!

Thanks guys!