Converting from V-6 front mounts to V-8s is not all that difficult, just laborious and time consuming. You won't be able to use anything from the V-6 configuration. That said, the clamshell style mounts can be sourced, starting with your local salvage/recycler or pick a part, and moving up the line to brand new, and/or high performance Getting the old ones off is a function of what ever tools you have available to you. Fastest method is a 4-1/2 Mini-grinder and a razor blade cut off wheel. Just cut away the nuts and the bolts will likely drop out.. If you plan to try to salvage the bolts, be careful, they could be metric and even if not will require 6 point sockets to avoid damaging them. I may have pictures somewhere of what the V-8 mounts look like when attached to the front crossmember. The only complication is the fact that the mounting bolts get put into position from inside out, meaning you have to fish them into the correct slots in the crossmember by a combination of extensions and swivels, or wrenches, one at a time, and then hold it in position until you can drop a nut onto it and run it down snug,x 3 per side. Check the slots for ability; you can sub 7/16ths capscrews for the metrics but may have to use a file to enlarge the slots ever so gently and minimally as possible.
You have dual head pipes that likely merge into one exhaust pipe somewhere near the cat or muffler located on the passengers side. As for choice of motor and transmission, as noted above, a donor car or a drive train pulled from a pick a part yard are among the variety of options. Most of the engine well wiring and tubing will re-route to attach to the 8 without too much modifying. You will need a different fan shroud as the V-6 version is deeper or longer than the V-8; rad should still be the same. There is enough cumulative experience lurking around on this site that help and pictures should be readily available to assist you.
Nick