Just wanting to switch out tanks (1975 245 tank w/ external fuel pump into a 1979 245 with internal fuel pump) and wondering if I have to do anything fancy or if it is not possible due to voltage, space and or psi requirements.....thanks, Archy

2 things

1-both have external pumps. the 1 on the 75 is the main pump, like the main pump on the tray with the accumulator on the 79. only the placement is different.

2-does the 75 tank have a drain plug? if so, don't use it. there was a campaign for YEARS on the 73-75 tanks. the plugs leak. the campaign might still be active. i know of someone who got a tank done in their 74 140 about 3 years ago.
if the plug is there, get the vin of the 75 and try to get the campaign done. of course, they will have to have the car. the dealer just can't hand you the parts no charge. but, this way you get a new tank free. if the plug is NOT there, then i think it's the same tank as the 79. the early cars required a bunch of parts to do a tank campaign. a dozen or so, not including clamps. but the 79 already has the good stuff on it. feed pump comes to mind, along with other stuff. good luck, chuck.