I used this one, with some modifications. The front pan seal 'lip' is cast into it.
http://kmjperformance.com/small-bloc...ion-plate.html
I removed the lip from the alum cover and used the 'lip' plate from this:
http://kmjperformance.com/sbc-chevy-...all-block.html
The holes in the alum. cover are pretty large. I made some spacers that locate into the recesses in the cover, used studs and 12 point nuts:
Worked out okay. Still have to remove the balancer to get the cam access plate off, though: