Hey, Jeff Mortenson from "Classic Chevy 5 Speed" has a tunnel replacement patch for use with the Tremec TKO tranny that might do the trick, but i'd think just a chunk of 18ga steel, cut and trimmed etc would do the trick (less $$$ too) as far as a bellhousing, clutch etc etc... yer not really limited on this like us 1st & 2nd genner guys are... we have ta stay pretty much with the 10.5 units because the bellhousing requirements of our vehicles... you can run a stock 11" bellhousing or a scattershield...
NOTE with the TKO (i'm sure the Richmond is same) IF you use a scattershield, the unit needs to be "dialed-in" with a dial indicator to ensure the opening is centered to the crank...
.005 is max yer allowed or tranny issues could be a problem...
Lakewoods definitely require it, McLeods from what i hear are generally spot on... but checking should be done anyways...
i hope i've helped you...
be Good !!!
