Sturdy and simple frame brace.
Y-axis belt roll holder with room for a nut and washer ( print them with 100% fill).
Drill 8mm holes in the middle of front, aft and center frame 20mm from the underside (the middle hole can be 10mm to give some extra play).
put a 40 cm 8mm thread bar through and 8mm nuts on both sides on all frame parts.
this setup take up the force from the belt just on the right spot and do not transfere the tension force to any other part of the construction.
The roll holder attachment screws need to be countersunked 3mm, with a 5mm drill, so they are flush with the surface, otherways they interfere with the front nut
You dont need to tear down the printer to install it, just put it on the side and drill the holes, it is a 5 min job, oh well...10 min then... !
1 pcs 40cm 8mm threadbar
6 pcs 8mm washers (not nessesery)
6 pcs 8mm nuts