Yes I will do something very similar.just do what burdekin said, drill the holes bigger then seam weld round them.
I had a challenge marking out the area where the box sits.so many different curves. The panel work is easily sorted.I could of got a smaller fuel cell but had what I had at that time.I wanted to keep it as low as possible. I new it would make contact with the crossmember. My plan is to use 45x60x4mm box section and fab a new one .I will mount it via spreader plates.I need to keep the original position of the axles mounting points.I will fab it around the bottom of the tank with mitre cuts.it will look like a u shape.should be strong enough. There is not a great load go through the back end.This all looks horribly familiar...
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I feel your pain.
Yes it's a tricky one to get right. I had it spot on a one point but it still didn't look right...it's a good place to mount tanks as it helps keep some weight over the back end.No going back is there? I think I must have measured and re-measured had a dozen times before committing with the grinder.
Painstakingly boaring Jim but needs must. A lot of corrosion between the seems...You're getting there mate, keep chipping away.