Can I change granny gear on my 1988 Trek mtb?

[thebaker]

I have an old 1988 Trek 830 mountain bike. Because it's pretty old, I don't want to put much money into it because it wouldn't take much cost to make it a better choice to buy a newer used mountain bike. Anyhow, the bike has sentimental value and still gets the job done so here is what I want to do.
The freewheel is a 14-32 six speed and it seems hard to find a replacement. I have many broken teeth on the 32 tooth large sprocket on the freewheel so I essentially do not have my lowest gear anymore. I'm thinking about changing the front granny chainring out from the existing 28 tooth to a 24 tooth. That way my granny gear with the second largest chainring on the freewheel (28 teeth) would give me a similar gear ratio to the lowest I had (actually slightly lower). The chainrings on this bike were "Ovaltech" and as the name implies quite oval in shape. I don't think this idea caught on to much but it's what I have and they have always worked fine for me. Can I just buy a 74mm bolt circle 24 tooth chainring and install it? Will this cause and shifting problems? I really don't care if it isn't the smoothest shifting bike as long as it does shift from granny ring to middle ring. middle ring is 38 teeth and "ovaltech" as well. Lastly, when I look at chainrings, Blackspire, I found one 74mm, 24T, that had a description "Designed for 8/9 speed drivetrains". Is there any reason this chainring wouldn't work on my six speed rear freewheel?
Thanks for any advice.
TheBaker

[DaveM]

As long as your crank has bolts to hold the chainrings on (not welded) you should be able to change out the granny gear without any major problem. I don't think the oval/round issue will matter.
However, if your freewheel has "many broken teeth" I'm guessing it's pretty old and probably due to be replaced anyway. Here (http://www.sheldonbrown.com/harris/freewheels.html#6) is an article about switching to 7 speed and here (http://harriscyclery.net/itemdetails.cfm?id=778) is a 7 sp freewheel 14-34.