The older cars originally had the CROSSPLY tyres many have been converted to radial, radial are much more modern and grip the road better.
It really depends if you want the original look or better safety?
Longstone tyres here in the UK can offer advice and do have a good selection, do consider your ground clearance and speedo inaccuracy depending on your tyres chosen!
https://www.longstonetyres.co.uk/classic-car-tyres/morgan/morgan-plus-4.html

Here is our 1956 Plus 4 fitted with Avon H M Tourist 5.00 / 5.25 - 16 max 29psi crossply tyres

[Linked Image]DSC_0005 by Robert & Ali Davies, on Flickr

Morgans 1934 MX, 1947 Series 1, 1956 +4 TR4, 2000 +4 T16
Triumph Herald 1969 13/60
Morris 1970