Budget D100 360 Suggestions

Holy chit that's some expensive prices for some of the machine work! But it is all realitive to not only where you live but who does the work. So, moot I guess.
I have not gone looking for Magnums. There in running trucks that cost triple on the cheap end of your listed high end. 2 wheel drives difficult to find. Also do realize that I live in an island and getting off requires a trip through NYC at a high cost. Starting at $15 a bridge. (Several bridges required. Or tunnels.)
This cost basically moots any cost savings between two way tolls and traffic driving. Which will drive you over the edge to NEVER do that again to save a buck!!!!

I currently have a Magnum ('00) in my Magnum ('79)

I'm not knockin what you suggest but I do scoff at the cost you think it will cost because of what you pay and think everyone else does or should or can.

The only draw back of the Magnum is intake selection and cam expense.
A refrains isn't always do able for all builds and purchasing EQ (or whatever) heads with a drilled LA pattern isn't always the answer. But it does seem to be for you.

Do note that I would rather build a Magnum block than a LA.