head gasket replacement

I have reinstalled and torqued the the head on my 94 850 wagon. In the process of reattaching everything, I just realized that I did not install the thermostat housing and now I cannot tighten down the bolts because the auxiliary bracket is in the way. I was going to take the head back off, but I was told that if it did I would have to use a new head gasket and head bolts. I could not uses the new ones that I just installed. (the motor has not been started) Is this correct? It looks easier to me to remove the head than to remove the auxiliary bracket. Or do I have to remove this bracket to install a new timing belt anyway? I have worked on cars(mostly British, jags, TRs, rovers and several BMWs, as a hobby before, but this is my first Volvo or front wheel drive car and I could use some help. Also, I could use some pointers on removing/ installing the timing belt. Please note: I have the Haynes repair manual, it seems to be ok, but not great. Thanks for your help.