Peavey Vintage 6x10 into bass combo

[bklee]

I have begun a project to convert a Peavey Vintage 6x10 guitar amp into a bass combo for use on small venues (coffeehouse or small club). I tried the amp (120W solid preamp, tube output stage w 4 6L6) bone stock at a medium volume full band rehearsal. Mids and highs were warm and satisfying; I used a Fender Jazz 5-string passive. But lows were flabby and an obvious stress on the 30+ year-old guitar speakers. Enclosing the back and replacing the speakers were necessary. The top two speakers had to be 8" so that the angled enclosure piece could clear the tubes and transformers which project downward. I didn't want a separate head setup (a la Ampeg flip-up) for convenience reasons so some elaborate (for me) cabinet work was called for. Long story short(er), the two 8-ohm 8s are wired parallel for 4 ohms on the external speaker jack, the four 4-ohm 10s are wired series-parallel for 4 ohm to the main jack. Total amp load is a permissible 2 ohms. Speakers are good Carvin Neos.

Two issues have arisen so far. The first is porting or not porting. One amp builder I talked to said leave a 3/4 inch slot at the bottom of the cabinet, but thumbnail calculations make that look too small. They seem to want a couple of 4-inch holes, but my math may be way off since I don't have exact numbers to work with. I cut two 3-inch holes with swinging plywood covers to vary the size empirically (they rattle, of course) until it sounds OK. The second issue is electrical: the amp builder I talked to also suggested that the cap on the bass control might want to be 0.1 mFd instead of 0.01 mFd to better support bass frequencies. Another amp guy said it should be OK with the original cap.

Sorry for the long post, but can anyone help me with these? This project is definitely worth doing for me because the combo is quite portable (heavy, though) with a handle on the long side so it can be carried like a suitcase (with a body in it).