D176 is the current mount for these saws. Fits midsize Echos and Poulans as well as the 10-series Macs.
A large mount Husky bar will fit on these saws, but I'd be very skeptical about it oiling right, at least without modification. The 10-series saws oil through the adjuster holes on D276 and D176 mount bars. If trying a D009 or D005 type bar, be SURE to check to see if the oil passage on the bar pad of the saw matches up with the oiler hole on the bar. Modification may well be necessary...
Kevin that muffler is missing a loovered outlet cover. Looking in the IPL you can see that there were three muffler types used on that saw. The one that's on there is by far the loudest of the three. That muffler is most often seen on the earlier 54cc 10-10A's and such. They are indeed LOUD. Both the 'reed type' flat muffler and the 'L shaped' muffler also shown in the IPL are quieter. Most of the 70cc saws have the 'L' shaped muffler. The muffler that was on your 805 is a much larger, more complex type with a large spark screen tower. Those were only used on the later 82cc saws.
IPL:
http://www.mymowerparts.com/pdf/McCulloch-Parts-Service-Repair-Manuals/Gas_Powered_Chain_Saws/McCulloch-Gas-Chain-Saws-Parts-Manuals-12-600033F-PRO-MAC-555-03-77-to-12-78-IPL-93712-R2.pdfThe 28" b/c's were mostly put on those smaller 10-series saws for brush and 'bumping knots'. The 54 and 57cc saws in the series will run a 20" bar very well, even in hardwoods. The 70cc saws are much stronger (as Al said) and can run a 24" bar in hardwoods no problem (and can run a 28" if you're not too heavy handed with them). The 82cc 10-series saws are in another league...