Morris Minor Owners Club

About 5 years ago I bought a Morris Minor Convertible fitted with a 2l Vauxhall Carlton engine, originally a 1098 Ser V, 2 door saloon.

Fun motoring for 5 years but now my mechanic and I are wondering about the structural capability of the conversion. The car has always been slightly bowed (gap at top of door is larger than at bottom and, looking along the sill, at the back of the door is larger than at the front) and has also flexed a lot during travel. There is a query as to whether the "bow" is currently more pronounced. Certainly now there seems to be permanent movement which is affecting the shape of the car, specifically:
The NS passenger door recently had to be reset to make it latch securely
The Front OS wing is showing signs of distortion which I am fairly sure is not impact related.

The conversion appears to have included:
seam welding an angle iron along the top of the existing sills
welding triangular corners between the sill and the posts fore and aft
welding additional plates along the underside at each side, between the sills and the rear suspension mountings
welding additional plates around the rim of the front wheel arches
probably more

Most of the welds appear to be structurally sound and there is no obvious signs of rupture or tearing. however, we are concerned that the conversion may have left a weak point, likely at the front of the sill, towards the front wheel arches, which needs strengthening.

Can anyone advise:
What is the best way of identifying the weak spot and the location for any strengthening?
Is there a plan which identifies the locations which should be strengthened when completing a conversion? Something that we can compare the existing work against?
Is there any other way in which anybody could help/advise in resolving this issue?
If not anybody likely to view this thread, who could I go to for (free if possible) advice?

there is one brace that I cant see you mentioning, the one inder the dash to the A pillar but that wont give those symptons.
if you look down the chassis lags at the front can you see any curve apart from the usual? there is a diagram in the ring bound workshop manual to measure the chassis like you would on a carolina jig. This might be worth considering.

seam welding an angle iron along the top of the existing sills
welding triangular corners between the sill and the posts

These are standard features.

welding additional plates along the underside at each side, between the sills and the rear suspension mountings
welding additional plates around the rim of the front wheel arches

These are not and could represent patches over/replacing corrosion.

A good test of structual condition would be to measure the door gap at the top whilst jacking up in turn the front, rear and centre of the car on each side. Any differences in the percieved gap would help locate the problem. In most cases weakening of the convertible structure results in the space within the wheelbace sagging and the door gap reducing. A widening gap could suggest that the conversion was done on a saloon that wasn't braced correctly when converted and stresses were built into the structure that are now releasing as a result of decay elsewhere.
I have had two convertibles. One was a converted saloon which had all the 'original' soft top strengthening panels and had been restored in my ownership but it's flexibilty meant I sold it as I wanted a modified car and I knew it couldn't take the punishment. My present car has uprated suspension, disks and 1275 and although it does show a very small degree of flexibility at the door tops the handling is not compromised in the least.

Probably need to take it a specialist such as JLH to get a knowlegable opinion. http://www.jlhmorrisminors.co.uk/

Please note I have edited my prevoius post to make my comments less confusing.