A few suggestions...
Plan on laying out $100.00 for the conversion. If you DIY, plan on half.
Both bikes have some style points, if you like those old racers, but neither are worth anything. Life as a cool fixie is just a way to show that old bike a new outlook.
The Brooks is not worth anything in disrepair, but if it is ridable, would add style points to the Raleigh.
The Peugeot, is it a road or MTB? For some reason I thought the Terran was an off roadie...It may have some strange thread sizes.
With all that said, I'd choose which ever frame has the best fit, condition and over all looks.
Post a couple of pic's and we'll be glad to chime in.