Welders don't like welding gas tanks with fumes in them - BOOM. It can be done filling tank with inert gas (CO2) . The high capacity tank I used is $125 plus the cap unique to tank. I didn't have to modify anything and trunk lid closes.
I have 2 914 engines and the bus flywheel that is needed. You can convert to Raby DTM up right cooling, joe Cali upright using T1/T4 cooling bits (there is abook available) or leave it the was it is - flat pancake pooling. Here picture I found of the flat engine in a Speedster replica.