Xray t2 09 Rebuild Help

[nivlacf1]

I am trying to rebuild an Xray T2 2009 the problem i am having is with the top deck supplied with the car. The motor bulk heads have to be on the furthest point forward to make the top deck fit but this results in front belt to lose and rear belt to tight, if i move it back to the furthest back position this then makes the top deck to short but the belts fit, i have 3 different size belts for front and rear, has anyone ever come across this and know what i maybe doing wrong, thanks