Yes an HP LaserJet 4 with PS card will work great with the MacPlus 6.0.8, the drivers readily available on the HP website will work.
FYI, you may want to maintain an old printer with your Plus depending on how much you use it. In my case, I only need to print occasionally and I use a printer which does not have drivers for a 512K. In the event you are interested, visit: http://www.mac128.com and check out printing from a 128K. Basically using the 6.0.8 printer driver, I am able to print a postscript file which will easily open and print from Mac OS X Preview, or PDF, formatted exactly as it was on your Plus to any modern printer.
FYI, you may want to maintain an old printer with your Plus depending on how much you use it. In my case, I only need to print occasionally and I use a printer which does not have drivers for a 512K. In the event you are interested, visit: http://www.mac128.com and check out printing from a 128K. Basically using the 6.0.8 printer driver, I am able to print a postscript file which will easily open and print from Mac OS X Preview, or PDF, formatted exactly as it was on your Plus to any modern printer.