Although both 'AndrewBrown' and 'guitarman' are correct in what they say, I would argue with 'guitarman' over the 1 series cars' towing abilities, 'edmundator'. Back in the day, we towed successfully with both a 145E and DL variants. The 'E' (injection) especially aquitted itself well.
As Andrew says, 1976 puts you firmly into 2 series territory. Once again, our experience is that they also tow well. From choice, I would opt for a 2.3 GLT variant, preferably with the 4 speed plus o/d gearbox, over 2.1 DLs.
Although projects in both series can still be found, cars in good condition - especially 1 series - are less common and generally command strong prices.
If you could live with a slightly later car, I would recommend a 7 series (1984 - 1991), again with the 2.3 motor. Once again, while manual + o/d is preferred by most, we have towed successfully with an automatic
fitted with an external transmission oil cooler.
Such cars also have the advantage of still being available in reasonable numbers at affordable prices, although prices for really nice ones have recently shown an upward trend. Examples are often to be found listed for sale in these forums.
This is just my personal view based on over 30 years of Volvo ownership; others may - and probably will - differ. I hope that it may help you to find a car that meets your requirements.
Regards, John.
PS - If you would still like a 1 series and could live with a saloon, the 164, with it's 3 litre straight six engine, would make an excellent classic tow car. I believe that a very few 165s (saloon conversions (?)) were also produced, but I have never seen one. J.