I'd be interested to hear from experience on this too. I've got a 59 261 sitting beside my 53 150 sedan. My 261 came out of a '50 truck and appears to have been front plate-mounted. I'm debating whether to use that or adapt the stock high side mounts.
I managed to scrounge up this pic on the HAMB.
This guy used his stock (53?) mounts cut down and fabbed a triangular adapter plate. You can certainly see the triangle mount for the late block and the top hat from the early side mount. Not entirely clear what the bottom bit is but I think its the part with the old bolt pattern that gets tossed out.
From the image one would guess either A: this didn't work; or B: the late triangle side mounts and the 52-54 high-side mounts are in the same location on the block (ie: this locates the engine under the hood so that the bell housing mounts fall in the right place and the engine doesn't end up through the radiator on the one hand and firewall on the other.)
I never payed much attention to the mounts on my 230, so I can't speak to that without looking.
