As of August 1, I will have approx 75 total nights combined between Marriott and SPG. Their website is currently broken, so I can't get an exact accounting, but I think it's something like 34 SPG and 41 Marriott.

If I plan my stays for the rest of the year to reach 50 in each program before December 31, will this qualify for two years of Platinum status for lifetime purposes?

I am currently at 5, so no matter what I have no way of qualifying for Lifetime Platinum before the end of this year, but if I can take one less year, it might be a good strategy nonetheless.

I also have Hyatt Globalist (and will be at 57 nights as of August 1), so, realistically this would be a deciding factor in switching my stays for the rest of the year from Hyatt to Marriott/SPG.