You also need to realize that you can’t just replace the 7 speed freewheel. You will need to add a spacer to the drive side and remove the same amount from the non-drive side to compensate for the wider freewheel.
Depending on the rear hub, there might be wider spacers and you may need to get a number of different widths and mic-n-match to get it correct. You’ll also need to re-dish (re-center) the wherl since the spacers have thrown that off.
John