Engine mounts 318 - 360
You CAN do it without a welder. The first time around from 273 brackets to 360, I did this:
Took one of the 360 mounts "for a pattern" and bolted it "other way round" to the pass side 273 mount to provide a jig to drill the extra hole
On the driver side, I added a piece of scrap strap down alongside the mount and up to the block ear, drilled holes, and bolted the whole thing together
(Later went to spool mounts which are about 1000000 times better design)