Fuel injection or aluminum heads

Neither.
Both come with unanticipated costs. If your budget is tight, save the dollars until you can afford both - then do one.

Heads are likely to require new pushrods, or rockers, or both. When I did my TF heads, I planned to re-use my rockers. Didn't work out. So another $750 for rocker kit and new pushrods. Then there's also the cost of the fluids, gaskets, sealer, etc. Plus, those heads might not do much for you anyway other than reduce weight (especially in the wallet area). Are they even actually available? Every time I've tried to buy MP parts, I get my order cancelled and told not available. Also, wisdom back in the day was that they're just re-boxed edel heads anyway. So also budget a few hundred to check springs, guides, seals, etc.

EFI is likely to require additional wiring, wiring changes, fuel pumps, tanks, lines, filters, hose ends, etc. You can easily spend another $500-1500 over the cost of the sniper kit just to get the EFI working. I have an FItech system with an in-tank pump, tanks-inc tank, and ran a new 3/8 hard line and use the original feed as my return line - all of which cost over and above the cost of the EFI kit. Then there was the AN hose ends, new fuel line, and I did my own wiring conversion to add a relay and power the pump. I even had to upgrade my alternator to get the idle voltage up enough to keep the pump happy. Like I said, lots of unanticipated supporting changes needed.

If the plan is to do it one piece at a time, go for it. But if you're trying to do a weekend swap with a price-point in mind, it rarely goes that route. Just sayin'.