here is another idea thats worth giving a shot:
try to install honda's deluxe's shock bottles to GS-150 shock shafts/rods. I am thinking since their outer dia is the same, there is a very high probability that they employ same oil seal inside. or any one of the honda/suzuki oil seals can be retrofitted, solving the problem of the shock mounting that you are facing.
if you can pull it off, all your worries will be gone. you will not have to change anything.
p.s. if you ask me, my first recommendation would be that you get a machinist and ask him to make new shock bolts. the bolts should be for GS150 from outside and from inside machined to be compatible with Deluxe.