Take pan loose and move it back out of the way , block it up as high as possable, close the seives ,lay some thin plywood on them and squeeze on in there and have at it. I'm 6' and 250n and it was tight in my 750 but I fit. Have fun.
You should be able to get at the front ones without moving the walker pan. To get the rear ones undo the pan blocks and slide the pan forward. When you put the blocks back together make a metal plate the same size as the bottom of the bottom block about 3.5"x3.5" and drill four holes in it to match the bolts coming through the block. The plate doesn't need to be very thick,1_16" will do nicely. Bolt this plate to the underside of the bottom block and put loctite on the bolts to keep the nuts from coming loose over time. If you do this you will never have block problems again, Even if the block cracks it can't come out of place and will still function perfectly.
If you dont like to disturb the pan blocks, undo the pitman crank bolt and rotate the crankshaft over centre, you can then reach the back walker blocks to adjust them . Muck quicker than taking the pan bolts out.