1995 Isuzu Rodeo Question replaceing the tranny

I recently purchased a tranny for my rodeo due to the old one not shifting. The dealer was going to charge an arm and a leg to troubleshoot and repair. I found one cheap at a local juckyard. During the removal of the old one, I found it extremley DIFFICULT to remove the torque converter even after the tranny was removed on the count of that dustplate. The 3 bolts are almost inaccessable. My question is can I install the new torque converter first, than the tranny?? A mechanic told me it was not recommended because I might damage the seal. Im afraid I may not be able to bolt the converter to the flywheel if I install the tranny first. Please help!!!