Gosh, version 3. Not something I have installed anywhere these days and no copy to hand to double check this but ...
I think all you need to do, after you have ensured you have a backup copy of the model and if all the other fields are in the right place when the model is applied, is open the report, the model and the template. Click on the template field position that you need to change, delete the field and the add it again in its new position or with its new size and so on.
Give it the same name and, assuming nothing else has changed, all should be well. If the field is used in any calculations you may want to consider whether the calculations are affected by the change - probably not I would think.
When happy, save the model with a new name or the old name if you have a secure backup somewhere (just in case ...) and all should be well.
I have assumed that the template trap is still working as expected. If the trap is also affected by the change then you may need to review that as well.
I hope this helps.
If not let us know and I am sure someone can be more specific - especially if they have a running copy of V3 available, as I think some do. The oldest version I have installed is V5.