I think I have decided to use a Continental IO-550 engine. The engine mount bolts for the TCM engines come through the firewall in the lower corners, and the standard header tank interferes with that location. So I have to modify my beautiful header tank by cutting the corners off.
The cut line was marked, and the oscillating tool made short work of the cuts. Two thick lay ups (8x bid) were used to make the new corner walls. These were coated, sanded, and coated with EZ-poxy to form a fuel-tight inside wall, then were bonded to the header tank with a fillet of cabo and 2x bid around the perimeter. New mounting ears were also added.
The sump tank halves were bonded with Jeffco and cured. The edge lip was sanded down and the entire tank was sanded and coated with 3 coats of epoxy. Slight pressurization with nitrogen caused the back panel to bow out a little bit, but I did not detect any leaks. The tank mounting ears were glassed onto the sides of the tank, and after curing, were trimmed. Finally, the fittings were screwed into the tank, and the tank was installed against the engine bulkhead below the main spar.
An inner flange to assist with joining the two halves of the sump tank was constructed by making a plywood sheet with a cutout slightly smaller than the opening in the tank. The inner surface of the plywood was covered with duct tape for release. Working inside the lip of the plywood, 2x BID was laid up inside the tank edge and onto the plywood.
I let this cure a couple of days before trying to remove the plywood sheet.
The factory supplies the two halves of the sump tank. Mine had harping pre-installed for the two fuel inlets and the fuel outlet to the engine. I had to install the hard points for the vent, the sump drain, and the float switch.
The entire inside of the tank was sanded to prepare for sealing and also for the hard points, which were glued in with cabo paste, filleted, and the covered with 2x BID.