Without further research the best you can say about the 1797 marriage in Marston Moretaine is that it's possibly the couple who subsequently baptised children in Toddington, 8 miles away.
For
- it's the only marriage on the IGI that fits (never a good reason!)
- timing is good as they baptised one child in MM in 1797, with the first baptism in Toddington in 1799
- there's a Joseph Evans age 77 buried in Toddington on 13 Apr 1850 which ties up pretty well with the Joseph Evans who was baptised on 22 May 1774 at MM
- there's a Mary Evans age 48 buried in Toddington on 23 Sep 1822, but no Mary Hart baptised in either Toddington or MM. The nearest seems to be at Wootton in 1774, 3 miles from MM.
- there's no burial of a Joseph or Mary Evans of the right age in MM, nor any further children baptised in MM, so they presumably moved away from MM.
Against
- they may have married and come from outside Beds (but see below re 1841 where who is presumably Joseph, gives his birthplace as Beds)
- there's nothing definite linking the MM couple to the Toddington pair.
Joseph appears to have remarried after the death of Mary in 1822 - there's a marriage on the IGI at Toddington on 23 Jun 1823, Joseph Evans and Jane Worker
In 1841 in Toddington, HO107/5/34/3 folio 12
Joseph Evans 69 ag lab
Jane Evans 60
Charlotte Worker 20 straw plaiter
All born Beds
As a rule of thumb, if you really need someone to be alive in 1851 so you can find their birthplace, you can guarantee they'll die a few months before. And Joseph is no exception! Buried April 1850.
Your best bet is to go through Toddington parish chest to see if there is a Settlement Certificate from MM to Toddington. I've looked at
http://blars.adlibsoft.com/ but drawn a blank. The relevant film number is 1597495 which can be ordered from and viewed at your nearest Family History Centre of the LDS - a full list can be found at
www.familysearch.org. You might also consider contacting Bedford and Luton Archives and Records Service to see if they have a will for Joseph's putative father, also Joseph, who may died in either 1788 or 1782 in MM
David