I would like to convert my 1994 airbag -equipped 945 Volvo to use
either the M-46 and overdrive gearbox or the M-47 5 speed gearbox. Is it possible? Where can I find all the parts I would need? Would it be possible to get them from a 745 originally equipped with a manual gearbox? Would the airbags present problems with the pedal assembly? Any advice about this topic
would be greatly appreciated.

Check the 740/940 FAQ. I do not believe that this replacement will present any sort of problem or interference with the airbag on either side. You will need a donor flywheel that has the correct ring on it for the flywheel sensor. The last year with an 740 NA manual in the US was 90. That would have been a M47. The last year for a 740 turbo manual was 91. They are both rare. Canada got manuals right up the end of the run. There was an '89 on EBAY with an M46 last week up for parts for $250. There were no takers. The car was/is located in Maryland.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7973005523&ssPageName=STRK:MEWA:IT

I have considered this conversion off and on. But the right opportunity has not presented itself.

Good luck,
Henry