Hi David. I remember St Martins church well and it's 2 graveyards. I lived on Victoria Street 1956 - 1959 and went to the Girl Guides at the church which was just opposite the end of Victoria Street. The 2 graveyards are in Garmston Street off Hungate behind the Cheese Shop, just the slabs used as paving which I used to walk through going to school at St Martins school 59 - 60
https://www.youtube.com/watch?v=itWQOvFWq6s and another graveyard at the bottom end of Beaumont Fee which was used as an overflow burial ground for St Martins up to 1850. It was mainly the graveyard for St Mary Crackpool (long gone)
https://heritage-explorer.lincolnshire.gov.uk/Monument/MLI89657 I hope you enjoy your trip
Penny