I have been running websites with frames for about 10 years, but I want to switch to iframes

My sites have galleries and use a simple frameset
<frameset cols="155,*">
  <frame src="462th.htm" name="th" scrolling="yes" noresize="noresize" />
  <frame src="462Body.php" name="body" />
Your browser does not handle frames! Please Enable them or update your browser	

Called by example 
    <a href="72009.php" target="body"><img src="thumbs/t_72009.jpg" width="120" height="80" alt="72009" />72009</a>
which I want to convert to iframe
I have stumbled around and got this far
 <iframe src="http://www.britishsteam.com/if_br/4-6-2/462th.htm" style="border:1px #666666 solid;" id="iframe_tm" scrolling="yes" 
 align="left"  height="720" width="150">
 <iframe src="http://www.britishsteam.com/if_br/4-6-2/462body.htm" style="border:1px #666666 solid;" id="iframe_content" height="720" width="95%">
as a basis, and I want to call links from id=iframe_tm to load in id= iframe_content

I have tried various ways but they always end up in a new browser tab eg:
<iframe src="70002.php" target="id=content"><img src="thumbs/t_70002a.jpg" width="120" height="80" alt="70002" />70002</a>
<iframe src="70002.php""target="content"><img src="thumbs/t_70002.jpg" width="120" height="80" alt="70002" />70002</a>

will show you where I am at to date, click on any thumb which should load into id= iframe_content ??

Any assistance would be most welcome