While the subframe mounts could be a problem, the place I'd begin looking is the Chevy V8. Check your hot rod how-to books and you'll find the 350 Chevy V8 and a 350 automatic transmission (I assume that's what has been swapped in) weighs about 675#, maybe a bit more if all the cast iron manifolds are still on and not replaced by lighter aluminum parts. Add in the extra weight of a HD radiator and its coolant and you've added maybe a couple of hundred extra pounds to the front end. I think that's why some folks choose the Ford 289/302 for a swap. They are longer than a Chevy but about 150# lighter at the start.

You may need to install springs for a 280SE 4.5 to carry the extra weight. Also, make sure the shocks are still Bilsteins or other OEM high pressure gas equivalent all around. They add a bit of spring rate to the suspension and if one end (rear) is gas and the other is not, you'll get a rake to the car's stance. Happened to me on my old 230/8 back when I was real new to MBs and did not understand their high quality parts. Put on standard Monroe shocks up front to save $$ and got a slight hot rod rake for no extra charge.

Good luck,

230/8

edit: Just read your post which came up as I was composing mine...if you have leaf springs then you will need to do some serious work to get it back to something resembling original. Good luck, indeed. You'll need it methinks.

230/8