Raleigh Montage mountain bike crank question Will a modern Shimano crank set be compatible to replace an oval tech Shimano set from the 1980’s.

It’s for a Raleigh Montage Mountain Bike.
Shimano make a number of triple cranks for 7 or 8 rear speeds. These can be found in Shimano's Acera, Altus and Tourney lines.

The chainline standard for triple cranks is 47.5mm (chainine is how far the center of the middle ring is from the center line of the frame, see here for details). I'm guessing an bike from the 80's might have used a narrower chainline. If possible, measure the chainline of the original crank. If it's within a few mm of 47.5mm a modern triple crank will work.

I think the chainring spacing should work fine with the Suntour thumb shifters. I'm guessing the front shifter isn't indexed, or has many index points for fine adjustment of the front derailleur. 

You will need to replace the bottom bracket along with the crank. 'Three piece' cranks for a square taper or Octalink axle need a specific axle length to get the correct chain line. The Montage has a square taper axle but it's very unlikely to be the correct length for a replacement crank.

From what I can tell the Montage frame has a standard 'English' threaded (1.370" X 24 tpi) bottom bracket shell. You will need to check the width, it should be 68mm, if it is, a new cartridge bottom bracket will fit.