Here is some info on the 1570/5 to GMT conversion:
https://rwg.cc/topic/114671-rolex-1575-gmt-movement-questions
Parts needed to convert 1570 w/date to GMT:
#8038 - center second pinion 5.70mm
#8037 - Cannon Pinion 3.39mm
#8039 - double tooth hour wheel 2.44mm
#8040 - 24hr wheel 1.41mm
#8035 - Calendar Wheel nut
#8036 - Date Jumper
#8006 - Yoke for cam
#8008 - spring for cam yoke
#8011 - stud for cam
#8030 - Center wheel with Cannon Pinion (or just the center wheel if you have the CP listed above).
#8034 - Calendar wheel (same as date movement afaik).
8034, 8035, and 8011 are listed in a group on the Rolex sheets.
The calendar spacer is not listed, p/n 7965 (iirc there is more than one p/n for this part).
Plus two cases of Jack Daniels and about $2000 as I have said before.
Shimming the date disc seat (calendar spacer) would be the low $$ way to go. The difference between the two movements is about 0.17mm overall and iirc the GMT spacer is about .1mm thicker than a regular date spacer.
In reality the sweep second pinion is the same for no date, date, and GMT movements...the tubes on the second hands are made longer for the date movement and longer still for the GMT movement. Hard to find a GMT length ss hand in aftmkt parts although some aftmkt ss hands come with long tubes and they need to be shortened for date and no date movements.
There is also an aftmkt 'shortcut' GMT kit for a 1570/5 to GMT conversion with a modified minute wheel that has a 24 hour drive gear added to it plus a 24 hour wheel but you still need the genuine GMT canon pinion, hour wheel, and center wheel to give enough room for the 24 hour hand between the dial and 12 hour hand. Might need to space the dial up a hair too. The 24 hour wheel fit (on top of the 12 hour wheel) is usually a bit sloppy and I have not seen these kits for sale in a few years. If they were properly made, they would have been a little better.
Here is a picture of a shortcut kit (top pic):
https://rwg.cc/topic/141303-cal-1570-gmt-tell-me-if-i-m-wrong/
Hard to believe the picture is still up.