You can not work with only the rear trunnion bolts! You have to loosen the front also, and pivot on the front center bolt.
remove 4 bolts
Leave the center ones just slightly loose and see if you can rotate the arbor and carriage assembly by hand to get the blade parallel to the miter slot.
It if will line up, then tighten the 2 center bolts. Then insert the remaining bolts one at a time and snug them up, then give everything a final 1/4 turn more.
If it won't line up using the 2 center bolts, your trunnion holes will have to be slightly enlarged and you need to figure out from the top down which way to elongate the holes. It won't take more than a few stokes of a 3/8" round rat tail file, but it will mean either removing the trunnions or dropping the whole assembly down. If you need to drop the whole assembly it's a good time to really clean out and wash the trunnions from any old grease and dust. Also remove any addition loose parts to reduce the weight.
If possible turn the saw upside down on it's table....yeah, I know it's a PITA, but this is a one time only process and you may as well do it right.... Been there, done it myself. It's also much easier to see which way to enlarge the holes and which ones upside down. Use star washers under the bolts and you'll find a 3/8" ratchet with a 12" extension will make life a whole lot easier.
Now, to align the blade to the slots turn the saw on it's back end, so you can see the bolt holes and still measure to the miter slots. I use a tri-square set to the closest dimension possible and check front and back on the same tooth rotating the blade. Once you get the same reading, again tighten the center bolts and replace the outer ones and tighten them also. RECHECK for parallelism.